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Astronomy Picture of the Day |
APOD: 2009 February 5 - NGC 604: X-rays from a Giant Stellar Nursery
Explanation:
Some 3 million light-years distant in nearby spiral
galaxy M33,
giant stellar nursery
NGC 604 is
about 1,300 light-years across,
or nearly 100 times the size of the
Orion Nebula.
In fact, among the star forming regions within the Local Group of
galaxies, NGC 604 is second in size only to 30 Doradus,
also known as
the Tarantula Nebula in the
Large Magellanic Cloud.
This space-age
color composite of X-ray data (in blue hues)
from the Chandra Observatory, and
Hubble optical data
shows that NGC 604's cavernous bubbles and cavities are filled with a
hot, tenuous,
X-ray
emitting gas.
Intriguingly, NGC 604 itself is divided by
a wall of relatively cool gas.
On the western (right) side of the nebula,
measurements
indicate that material is likely
heated to X-ray temperatures by the energetic winds
from a cluster of about 200 young, massive stars.
On the eastern side the X-ray filled cavities seem to be older,
suggesting
supernova explosions from the end of
massive star evolution contribute to their formation.
APOD: 2009 January 31 - Simeis 147: Supernova Remnant
Explanation:
It's easy to get lost following the intricate filaments in this
detailed image of faint
supernova remnant Simeis 147.
Also cataloged as Sh2-240 and seen towards the constellation
Taurus,
it covers nearly 3 degrees (6 full moons) on the sky.
That corresponds to a width of 150 light-years at
the stellar debris cloud's estimated distance of 3,000 light-years.
The remarkable narrow-band composite image in the
Hubble color palette
includes emission from hydrogen, sulfur, and oxygen atoms
tracing regions of shocked, glowing gas.
This supernova remnant has an estimated age of about 40,000
years - meaning light from the massive stellar explosion first
reached Earth 40,000 years ago.
But this expanding remnant is not the only
aftermath.
The cosmic catastrophe
also left behind
a spinning neutron star or pulsar,
all that remains of the original star's core.
APOD: 2009 January 8 - NGC 2736: The Pencil Nebula
Explanation:
This shock wave plows through space at over 500,000 kilometers per hour.
Moving right to left in the
beautifully
detailed
color composite, the thin, braided filaments are actually
long ripples in a sheet of glowing gas seen almost edge on.
Cataloged
as NGC 2736, its narrow appearance
suggests its popular name,
the Pencil Nebula.
About 5 light-years long and a mere 800 light-years away,
the Pencil Nebula is only a small part of the
Vela
supernova remnant.
The Vela remnant itself
is around 100 light-years in diameter, the expanding
debris
cloud of a star that was seen to
explode about 11,000 years ago.
Initially, the shock wave was moving at millions of kilometers
per hour but has slowed considerably, sweeping up
surrounding interstellar gas.
APOD: 2008 December 19 - The Large Cloud of Magellan
Explanation:
The 16th century Portuguese navigator
Ferdinand
Magellan and his crew had plenty of time to study the
southern sky during the first circumnavigation of planet Earth.
As a result, two fuzzy cloud-like
objects easily visible to southern hemisphere skygazers are known as the
Clouds of Magellan,
now understood to be
satellite galaxies of our much larger, spiral Milky Way galaxy.
About 160,000 light-years distant in the constellation
Dorado,
the Large
Magellanic Cloud (LMC) is seen here in a remarkably detailed,
10
frame mosaic image.
Spanning about 30,000 light-years or so, it is
the most massive of the Milky Way's
satellite
galaxies and is the site of the
closest
supernova in modern times, SN 1987A.
The prominent reddish knot near the bottom is 30 Doradus, or the
Tarantula Nebula, a giant star-forming
region in the Large Magellanic Cloud.
To identify the location of the supernova and navigate your way
around the many star clusters and nebulae of the LMC, just consult this
well-labeled view.
APOD: 2008 November 1 - A Spectre in the Eastern Veil
Explanation:
Menacing
flying
forms and garish colors are a mark of the Halloween season.
They also stand out in
this
cosmic close-up of the eastern Veil Nebula.
The Veil Nebula itself is a
large supernova remnant, the expanding
debris cloud from the death explosion of a massive star.
While the Veil is roughly circular in shape covering nearly 3 degrees
on the sky in the constellation Cygnus, this portion of the eastern
Veil spans only 1/2 degree, about the apparent size
of the Moon.
That translates to 12 light-years at the Veil's
estimated distance of 1,400 light-years from planet Earth.
In this composite of image data recorded through
narrow band filters,
emission from hydrogen atoms in the remnant is shown in red with strong
emission from oxygen atoms in greenish hues.
In the western part of the Veil lies another seasonal apparition,
the Witch's Broom.
APOD: 2008 October 21 - A Dark Pulsar in CTA 1
Explanation:
Where's the pulsar?
Previously, the nebula
CTA 1 showed
an expanding supernova remnant, a
jet, and a point source expected to be a
pulsar -- a
rotating neutron star producing pulses at radio energies.
But no radio pulses were detected.
Now NASA's recently deployed
Fermi Space Telescope has solved the mystery with some of its
initial observations indicating that the point source is pulsing at
gamma-ray energies.
The strange source is the first of a class that might be
dubbed "dark pulsars", rotating
neutron stars
that appear to pulse only in high-energy radiations.
Such pulsars
might not be detectable in
radio
or visible light if they emit those radiations into a narrow
beam not seen from Earth.
If true, our Galaxy might have more pulsars left for
Fermi to discover.
Studying the gamma-ray properties of
pulsars gives
valuable clues to physics of the emission regions on neutron stars.
In this graphic,
the pulsar's position is indicated in the wider
CTA 1
supernova remnant.
An artist's illustration of the pulsar beaming at gamma-ray energies
is shown in the inset.
APOD: 2008 October 12 - Spiral Galaxy NGC 3370 from Hubble
Explanation:
Is this what our own Milky Way Galaxy looks like from far away?
Similar in size and grand design to our
home Galaxy
(although without the central bar), spiral galaxy
NGC 3370
lies about 100 million
light-years
away toward the constellation of the Lion
(Leo).
Recorded
above in exquisite detail by the
Hubble Space Telescope's
Advanced Camera for Surveys,
the big, beautiful face-on spiral is not only photogenic, but has proven
sharp enough to study individual stars known as
Cepheids.
These pulsating stars have been used to accurately determine NGC 3370's distance.
NGC 3370 was chosen for this study because in 1994 the
spiral galaxy was also home to a well studied stellar explosion -- a
Type Ia supernova.
Combining the known distance to this
standard candle supernova,
based on the Cepheid measurements, with observations of
supernovas at even greater distances,
has helped to reveal the size and
expansion rate
of the entire Universe itself.
APOD: 2008 September 15 - SN 1006: A Supernova Ribbon from Hubble
Explanation:
What created this unusual space ribbon?
Most assuredly, one of the most
violent explosions
ever witnessed by ancient humans.
Back in the year 1006 AD, light reached Earth from a stellar explosion in the
constellation of the Wolf
(Lupus),
creating a "guest star" in the sky that appeared
brighter than Venus and lasted for over two years.
The supernova, now cataloged at
SN 1006,
occurred about 7,000 light years away and has left a large remnant that continues to expand and fade today.
Pictured above is a small part of that
expanding supernova
remnant dominated by a
thin and outwardly moving
shock front that heats and ionizes
surrounding ambient gas.
SN 1006 now has a diameter of nearly 60
light years.
Within the past year, an
even more powerful explosion
occurred far across the universe that was visible to modern humans,
without any optical aid, for a few seconds.
APOD: 2008 August 19 - NGC 6960: The Witch's Broom Nebula
Explanation:
Ten thousand years ago, before the dawn of recorded human history,
a new light must suddenly have appeared in the
night sky and faded after a few weeks.
Today we know this light was an exploding star and record the colorful expanding cloud as the
Veil Nebula.
Pictured above is the west end of the
Veil Nebula known technically as
NGC 6960 but less formally as the
Witch's
Broom Nebula.
The expanding debris cloud gains its colors by sweeping up and
exciting existing nearby gas.
The supernova remnant
lies about 1400 light-years away towards the constellation of
Cygnus.
This Witch's Broom actually spans over three times the
angular size of the full
Moon.
The bright star 52
Cygni
is visible with the unaided eye from
a dark location but unrelated to the ancient
supernova.
APOD: 2008 August 11 - Black Hole Candidate Cygnus X-1
Explanation:
Is that a black hole?
Quite possibly.
The Cygnus X-1
binary star system contains one of the best candidates for a
black hole.
The system was discovered because it is one of the brightest
X-ray
sources on the sky, shining so bright it was detected by the
earliest rockets
carrying cameras capable of seeing the previously unknown
X-ray sky.
The star's very name indicates that it is the single brightest X-ray source in the
constellation
of the Swan Cygnus.
Data indicate that a
compact object
there contains about nine times the mass of the Sun and changes its
brightness continually on several time scales, at least down to milliseconds.
Such behavior is expected for a
black hole,
and difficult to explain with other models.
Pictured above is an artistic impression of the
Cygnus X-1 system.
On the left is the bright blue
supergiant star
designated HDE 226868, which is estimated as having about 30 times the mass of our Sun.
Cygnus X-1 is depicted on the right, connected to its
supergiant companion by a stream of gas, and surrounded by an impressive
accretion disk.
The bright star in the
Cygnus X-1 system is visible with a small telescope.
Strangely, the
Cygnus X-1 black hole candidate
appears to have formed without a bright
supernova explosion.
APOD: 2008 July 4 - SN 1006 Supernova Remnant
Explanation:
A new star, likely the brightest supernova
in recorded human
history, lit up
planet Earth's sky in the year 1006 AD.
The expanding debris cloud from the stellar explosion,
found in the southerly constellation
of Lupus,
still puts on a cosmic light show across the
electromagnetic spectrum.
In fact, this
composite view includes
X-ray data in blue from the
Chandra Observatory,
optical data in
yellowish hues, and radio image data in red.
Now known as the SN 1006
supernova remnant, the debris cloud
appears to be about 60 light-years across and is understood
to represent the remains of a white dwarf star.
Part of a binary star system,
the compact white dwarf gradually
captured material from its companion star.
The buildup in mass finally triggered a
thermonuclear
explosion that destroyed the dwarf star.
Because the distance to the supernova remnant is about 7,000
light-years, that explosion actually
happened 7,000 years before the light reached Earth in 1006.
Shockwaves in the remnant
accelerate
particles to extreme energies and are
thought to be a source of the mysterious
cosmic rays.
APOD: 2008 July 1 - Pickering's Triangle from Kitt Peak
Explanation:
Wisps like this are all that remain visible of a Milky Way star.
About 7,500 years ago that star exploded in a
supernova leaving the
Veil Nebula, also known as the Cygnus Loop.
At the time, the expanding cloud
was likely as bright as a crescent Moon, remaining
visible for weeks to people living at the dawn of
recorded history.
Today, the resulting supernova remnant
has faded and is now visible only through a small telescope directed toward the
constellation of
Cygnus.
The remaining Veil
Nebula is physically huge, however, and even though it lies about 1,400
light-years distant, it covers over five times the size of the
full Moon.
In images of the
complete Veil Nebula,
studious readers
should be able to identify the
Pickering's Triangle
component pictured above, a component named for a
famous astronomer and the wisp's
approximate shape.
The above image is a mosaic from the 4-meter
Mayall telescope at the
Kitt Peak National Observatory
located in Arizona,
USA.
APOD: 2008 June 17- Eta Carinae and the Homunculus Nebula
Explanation:
How did the star Eta Carinae create this unusual nebula?
No one knows for sure.
About 165 years ago, the southern star
Eta Carinae
mysteriously became the second
brightest star in the night sky.
In 20 years, after ejecting more mass than our Sun, Eta Car unexpectedly faded.
This outburst appears to have created the
Homunculus Nebula,
pictured above in a composite image from the
Hubble Space Telescope
taken last decade.
Visible in the
above image
center is purple-tinted light reflected from the violent star Eta Carinae itself.
Surrounding this star are expanding lobes of gas laced with filaments of dark
dust.
Jets bisect the lobes emanating from the central star.
Surrounding these lobes are
red-tinted debris
captured only by its glow in a narrow band of red light.
This debris is expanding most quickly of all, and includes streaming
whiskers and
bow shocks caused by collisions with
previously existing material.
Eta Car still undergoes
unexpected outbursts,
and its high mass and volatility make it a candidate to explode in a
spectacular supernova
sometime in the next few million years.
APOD: 2008 April 26 - The Tarantula Zone
Explanation:
The
Tarantula Nebula is more than 1,000 light-years in diameter --
a giant star forming region within our neighboring galaxy
the Large Magellanic Cloud (LMC).
That cosmic arachnid lies at the upper left of
this
expansive mosiac covering a part of the LMC
over 6,000 light-years across.
Within the Tarantula (NGC 2070), intense radiation, stellar winds and
supernova shocks from the central young cluster of massive
stars, cataloged as R136,
energize the nebular glow and shape the spidery filaments.
Around the Tarantula are other violent star-forming regions with
young star clusters, filaments and
bubble-shaped clouds.
The small but expanding remnant of
supernova 1987a, the closest supernova
in modern history, is located near the center of the view.
The rich field is about as wide
as four full moons on the sky, located in the southern
constellation
Dorado.
APOD: 2008 March 6 - Vela Supernova Remnant
Explanation:
The plane of our Milky Way Galaxy runs through this
complex
and beautiful skyscape.
At the northwestern edge of the constellation
Vela
(the Sails) the 16 degree wide, 30 frame mosaic is centered on the
glowing filaments of the
Vela
Supernova Remnant, the expanding debris cloud from the
death explosion of a massive star.
Light from the supernova explosion
that created the Vela remnant
reached Earth about 11,000 years ago.
In addition to the shocked filaments of glowing gas, the cosmic
catastrophe also left behind an incredibly dense,
rotating stellar core, the Vela Pulsar.
Some 800 light-years distant, the Vela remnant is likely
embedded
in a larger and older supernova remnant, the
Gum Nebula.
The broad mosaic includes
other
identified emission and reflection nebulae, star clusters,
and the remarkable
Pencil
Nebula.
APOD: 2008 February 17 - M1: The Crab Nebula from Hubble
Explanation:
This is the mess that is left when a star explodes.
The Crab Nebula, the result of a
supernova seen in
1054 AD,
is filled with
mysterious filaments.
The filaments are not only
tremendously complex, but appear to have
less mass than expelled in the original supernova and a
higher speed than expected from a free explosion.
The above image,
taken by the Hubble Space Telescope,
is presented in three colors chosen for scientific interest.
The Crab Nebula spans about 10 light-years.
In the nebula's very center lies a
pulsar: a
neutron star as massive as the
Sun
but with only the size of a
small town.
The Crab Pulsar rotates about 30 times each second.
APOD: 2008 January 18 - Supernova Factory NGC 2770
Explanation:
The stellar explosions known as
supernovae are
among the most
powerful events in the universe.
Triggered by the collapsing core of a massive star or the
nuclear demise of a white dwarf,
supernovae occur
in average spiral galaxies only about once every century.
But the remarkable spiral galaxy NGC 2770 has lately
produced more than its fair share.
Two still bright supernovae and the location of a third,
originally spotted in 1999 but now faded from
view, are indicated in this image of the edge-on spiral.
All three supernovae are now thought to be of the core-collapse variety,
but the most recent of the trio,
SN2008D, was
first
detected by the
Swift
satellite at more extreme energies as an
X-ray flash (XRF) or
possibly a low-energy version of a
gamma-ray burst on January 9th.
Located a
mere
90 million light-years away in the northern
constellation Lynx, NGC 2770 is now the closest galaxy known
to host such a
powerful supernova event.
APOD: 2008 January 17 - Thor s Emerald Helmet
Explanation:
This helmet-shaped cosmic cloud with
wing-like appendages is popularly called
Thor's
Helmet.
Heroically sized even for a
Norse god,
Thor's Helmet is about 30 light-years across.
In fact, the helmet is actually more like
an interstellar bubble, blown as a fast
wind from the bright, massive star near the bubble's center sweeps
through a surrounding molecular cloud.
Known as a
Wolf-Rayet star, the central star is an
extremely hot giant thought to be in a brief,
pre-supernova stage of evolution.
Cataloged as NGC 2359, the nebula is located about
15,000 light-years away in the constellation
Canis
Major.
The sharp
image captures striking details of the
nebula's filamentary structures and also
records an almost emerald color from strong emission
due to oxygen atoms in the glowing gas.
APOD: 2008 January 15 - Double Supernova Remnants DEM L316
Explanation:
Are these two supernova shells related?
To help find out, the 8-meter
Gemini Telescope located high atop a mountain in
Chile
was pointed at the unusual, huge, double-lobed cloud dubbed
DEM L316.
The resulting image,
shown above, yields tremendous detail.
Inspection of the image as well as
data taken by the orbiting
Chandra X-Ray Observatory
indicate how different the two
supernova remnants are.
In particular, the smaller shell appears to be the result of
Type Ia supernova
where a white dwarf exploded,
while the larger shell appears to be the result of a
Type II supernova
where a massive normal star exploded.
Since those two stellar types evolve on such
different time scales, they likely did not form together and so are likely not physically associated.
Considering also that no evidence exists that the
shells are colliding,
the two shells are now hypothesized to be superposed by chance.
DEM L316
lies about 160,000
light years
away in the neighboring
Large Magellanic Cloud (LMC) galaxy,
spans about 140 light-years across, and appears toward the southern constellation of the
Swordfish (Dorado).
APOD: 2007 October 16 - SN 2005ap: The Brightest Supernova Yet Found
Explanation:
What could cause a bang this big?
This
supernova explosion
was so inherently bright that it could be seen nearly 5 billion
light years away (a
redshift
of 0.28) even with a small telescope.
Specific colors emitted during
SN 2005ap
indicate that it was a
Type II supernova,
a breed of stellar explosion that results when a high mass star begins
fusing
heavy elements in or near its core.
Type II supernovas may be more powerful than their
Type Ia cousins,
but they are not currently more useful cosmologically because
astronomers don't understand how to accurately recover their
intrinsic brightnesses.
It is therefore dimmer
Type Ia supernovas
that are used by astronomers to calibrate the
distance scale
of the nearby universe.
Were Type II supernova
better understood, astronomers might be able to
probe distances
further into the universe, and so probe the stability of the strange
dark energy that dominates the present universe.
Pictured above
in a digitally compressed image, the bright supernova SN 2005ap is
visible on the right where no exploding star had been seen on the
left less than three months before.
APOD: 2007 September 24 - A Galactic Star Forming Region in Infrared
Explanation:
How do stars form?
To help study this complex issue, astronomers took a
deep image in infrared light of an active part of our
Milky Way Galaxy
where star formation is rampant.
In IRDC G11.11-0.11, thick clouds of
dust and gas are congealing into stars
that are so dark that humans living there would see an empty night sky.
The image, though, taken last year by the
Spitzer
Space Telescope in infrared light,
shows vast glowing fields of gas and dust,
indicating that much of this dust is heated by forming stars.
The centers of some clouds, such as the
snake-like structure
on the upper left, are so thick and cold that they are dark even in
infrared light.
Many of the red dots are glowing
dust shrouds
centered on very young newly formed stars.
The unusual red sphere below the snake is actually a
supernova remnant,
the glowing shell of a young star so massive it evolved rapidly and exploded.
The region spans about 150 light years and
lies about 10,000
light years
away toward the
constellation of Sagittarius.
APOD: 2007 August 22 - Tentacles of the Tarantula Nebula
Explanation:
The largest, most violent star forming region known in the whole
Local Group of galaxies
lies in our neighboring galaxy the
Large Magellanic Cloud (LMC).
Were the Tarantula Nebula at the distance of the
Orion Nebula -- a local star forming region --
it would take up fully half the sky.
Also called
30 Doradus, the red and pink
gas indicates a massive
emission nebula, although
supernova remnants and
dark nebula also exist there.
The bright knot of stars left of center is called
R136 and contains many of the most
massive, hottest, and brightest stars known.
The
above image taken with the
European Southern Observatory's (ESO's)
Wide Field Imager
is one of the
most detailed ever of this vast star forming region.
ESO has made it possible to fly around and into this detailed image by
clicking here.
APOD: 2007 July 24 - Spiral Galaxy M83: The Southern Pinwheel
Explanation:
M83 is one of
the closest and brightest
spiral galaxies on
the sky.
Visible with binoculars in the constellation of
Hydra, majestic spiral arms
have prompted its nickname as the Southern Pinwheel.
Although discovered 250 years ago,
only
much later was it appreciated that
M83 was not a nearby gas cloud, but a
barred
spiral galaxy much like our own
Milky Way Galaxy.
M83, pictured above, is a prominent member
of a group of galaxies that includes
Centaurus A and
NGC 5253, all of which lie about 15 million
light years distant.
Several bright supernova explosions
have been recorded in M83.
An intriguing double
circumnuclear ring has been discovered
at the center of M83.
APOD: 2007 May 10 - SN 2006GY: Brightest Supernova
Explanation:
The stellar explosion cataloged as
supernova
SN 2006gy shines
in this
wide-field image (left) of its
host galaxy, NGC 1260,
and expanded view (upper right panel) of the region surrounding
the galaxy's core.
In fact, given its estimated distance of 240 million light-years,
SN 2006gy was brighter than, and has stayed brighter
longer than,
any previously seen supernova.
The Chandra observations in the lower right panel establish
the supernova's x-ray brightness and lend strong
evidence to the theory that
SN
2006gy was the death explosion of
a star well over 100 times as massive as the Sun.
In such an exceptionally massive star,
astronomers
suspect an instability producing matter-antimatter
pairs
led to the cosmic blast and obliterated the stellar core.
Thus, unlike in other massive star supernovae, neither
neutron star,
or even
black hole,
would
remain.
Intriguingly, analogs in our own galaxy
for SN 2006gy's progenitor may include the
well-known,
extremely massive star Eta Carinae.
APOD: 2007 April 16 - MWC 922: The Red Square Nebula
Explanation:
What could cause a nebula to appear square?
No one is quite sure.
The hot star system known as
MWC 922, however, appears to be imbedded in a nebula with just such a shape.
The above image combines
infrared exposures from the
Hale Telescope on
Mt. Palomar in
California, and the
Keck-2 Telescope on
Mauna Kea in
Hawaii.
A leading progenitor hypothesis for the
square nebula is that the central star or stars
somehow expelled cones of gas during a late
developmental stage.
For MWC 922,
these cones happen to incorporate nearly
right angles
and be visible from the sides.
Supporting evidence for the
cone
hypothesis includes radial spokes in the image that might run along the cone walls.
Researchers speculate that the cones viewed from
another angle would appear similar to the gigantic rings of
supernova 1987A,
possibly indicating that a star in MWC 922 might one day itself explode in a similar
supernova.
APOD: 2007 February 13 - Vela Supernova Remnant in Visible Light
Explanation:
The explosion is over but the consequences continue.
About eleven thousand years ago a star in the constellation of
Vela could be seen to
explode,
creating a strange point of light briefly visible to humans living near the beginning of
recorded history.
The outer layers of the star crashed into the
interstellar medium, driving a
shock wave that is still visible today.
A roughly spherical, expanding shock wave is
visible in X-rays.
The
above image
captures much of that filamentary and gigantic shock in
visible light,
spanning almost 100
light years
and appearing twenty times the diameter of the
full moon.
As gas flies away from the detonated star, it
decays and reacts with the interstellar medium,
producing light in many different colors and energy bands.
Remaining at the center of the
Vela Supernova Remnant is a
pulsar, a star as dense as nuclear matter that completely rotates
more than ten times in a single second.
APOD: 2007 January 16 - Keplers Supernova Remnant in X Rays
Explanation:
What caused this mess?
Some type of star exploded to create the unusually shaped nebula known as
Kepler's supernova remnant,
but which type?
Light from the stellar explosion that
created this energized cosmic cloud was first seen on planet
Earth in October 1604, a mere
four hundred years
ago.
The supernova produced a bright
new star
in early 17th century skies within the constellation
Ophiuchus.
It was studied by astronomer
Johannes Kepler
and his contemporaries, with out the benefit of a telescope, as they
searched for an explanation of the heavenly apparition.
Armed with a
modern
understanding of stellar evolution, early 21st century
astronomers continue to explore the expanding debris cloud, but can now use
orbiting space telescopes to survey Kepler's supernova remnant (SNR)
across the spectrum.
Recent X-ray data and
images
of Kepler's supernova remnant taken by the orbiting
Chandra X-ray Observatory has shown relative elemental abundances more typical of a
Type Ia supernova, indicating that the progenitor was a
white dwarf star that exploded
when it accreted too much material and went over
Chandrasekhar's limit.
About 13,000 light years away, Kepler's supernova
represents the most recent stellar explosion seen to
occur within
our Milky Way galaxy.
APOD: 2007 January 7 - The Mysterious Rings of Supernova 1987A
Explanation:
What's causing those odd rings in
supernova 1987A?
In 1987, the brightest supernova
in recent history occurred in the
Large Magellanic Clouds.
At the center of the picture is an object central to the remains of the violent
stellar explosion. When the
Hubble Space Telescope was pointed at the
supernova remnant
in 1994, however, the existence of
curious
rings was
confirmed.
The origins of these rings still remains a mystery.
Speculation into the cause of the rings includes beamed
jets emanating from a dense star left over from the supernova, and a
superposition of two stellar winds ionized by the
supernova explosion.
APOD: 2007 January 1 - NGC 6960: The Witch's Broom Nebula
Explanation:
Ten thousand years ago, before the dawn of recorded human history,
a new light must suddenly have appeared in the
night sky and faded after a few weeks.
Today we know this light was an exploding star and record the colorful expanding cloud as the
Veil Nebula.
Pictured above is the west end of the
Veil Nebula known technically as
NGC 6960 but less formally as the
Witch's
Broom Nebula.
The rampaging gas gains its colors by impacting and
exciting existing nearby gas.
The supernova remnant
lies about 1400 light-years away towards the constellation of
Cygnus.
This Witch's Broom actually spans over three times the
angular size of the full
Moon.
The bright star 52
Cygnus is visible with the unaided eye from
a dark location but unrelated to the ancient
supernova.
APOD: 2006 December 24 - Rumors of a Strange Universe
Explanation:
Eight years ago
results were
first presented indicating that most of the energy in our universe is not in
stars or galaxies but is tied to space itself.
In the language of cosmologists, a large
cosmological constant is directly implied by new distant
supernovae observations.
Suggestions of a
cosmological constant (lambda) are
not new -- they have existed since the advent of
modern relativistic cosmology.
Such claims were not usually popular with astronomers,
though, because lambda is so unlike known universe components, because
lambda's value appeared limited by other observations,
and because less-strange cosmologies without lambda had
previously done well in explaining the data.
What is noteworthy here is the seemingly direct and reliable method of the observations and the good reputations of the
scientists conducting
the investigations.
Over the past eight years, independent
teams of astronomers have continued to accumulate data
that appears to confirm the unsettling result.
The
above picture of a supernova that occurred in
1994
on the outskirts of a
spiral galaxy
was taken by one of these collaborations.
APOD: 2006 November 24 - Alpha Cam: Runaway Star
Explanation:
Runaway stars
are massive stars traveling rapidly through
interstellar space.
Like a ship plowing through cosmic seas, runaway star
Alpha Cam
has produced this graceful
arcing bow wave or bow
shock - moving at over 60
kilometers per second and compressing the
interstellar
material in its path.
The bright star
above and left of center in this wide (3x2 degree) view,
Alpha Cam is about 25-30 times
as massive as the Sun, 5 times hotter (30,000 kelvins), and
over 500,000 times brighter.
About 4,000 light-years away in the long-necked constellation
Camelopardalis,
the star also produces a strong wind.
The bow shock stands off about 10 light-years from the star itself.
What set this
star
in motion?
Astronomers have long thought that Alpha Cam was flung out of
a nearby cluster of young hot stars due to gravitational interactions
with other cluster members or perhaps by the
supernova explosion of a
massive companion star.
APOD: 2006 October 26 - Composite Crab
Explanation:
The Crab Nebula is cataloged as M1, the first object on
Charles
Messier's famous list of things which are not comets.
In fact,
the
Crab is now known to be a
supernova remnant,
expanding debris from the death explosion of a massive star.
This intriguing
false-color image combines
data from space-based observatories,
Chandra,
Hubble, and
Spitzer,
to explore the
debris cloud in x-rays (blue-purple),
optical (green), and infrared (red) light.
One of the most exotic objects known to modern astronomers,
the Crab Pulsar,
a neutron star spinning 30 times a second,
is the bright spot near picture center.
Like a cosmic dynamo,
this collapsed remnant of the stellar core
powers the Crab's emission across the electromagnetic spectrum.
Spanning about 12 light-years, the Crab Nebula is
6,500 light-years away in the
constellation
Taurus.
APOD: 2006 September 28- RCW 86: Historical Supernova Remnant
Explanation:
In 185 AD,
Chinese
astronomers recorded the appearance of
a new star in the Nanmen asterism -
a part of the sky identified
with Alpha and Beta Centauri on modern star charts.
The
new star was visible for months and is
thought to be the earliest
recorded supernova.
Data from two orbiting X-ray telescopes of the 21st
century,
XMM-Newton and
Chandra,
now offer
evidence that supernova remnant RCW 86
is indeed the debris from that
stellar explosion.
Their composite, false-color
view
of RCW 86 shows the expanding shell
of material glowing
in x-rays
with high, medium, and low energies shown in blue, green, and red hues.
Shock velocities
measured in
the x-ray emitting shell and an
estimated radius of about 50 light-years can be
used to find the apparent age of the remnant.
The results indicate that light from the initial explosion
could well have first reached planet Earth in 185 AD.
Near the plane of our Milky Way Galaxy,
RCW 86 is about 8,200 light-years away.
APOD: 2006 August 29 - Supernova Remnant E0102 from Hubble
Explanation:
It's the blue wisp near the bottom that's the remnant of a tremendous recent supernova explosion.
The large pink structure looming to the upper right is part of N76, a large
star forming region in our neighboring
Small Magellanic Cloud (SMC) galaxy.
The supernova remnant wisp, with full coordinate name 1E0102.2-7219 and frequently abbreviated as E0102,
also lies in the SMC, about 50 light years away from N76.
The above image is a composite of several images taken by the Hubble Space Telescope.
E0102 is of research interest
because we see it as it appeared only 2,000 years after its explosion.
Examination of E0102 therefore gives clues about how an
enigmatic supernova
works and what materials it dispersed into the surrounding
interstellar medium.
APOD: 2006 July 28 - Four Supernova Remnants
Explanation:
These
four panels show x-ray images of expanding cosmic debris clouds,
tens of light-years across, in nearby galaxy the
Large Magellanic Cloud.
The supernova remnants (SNRs) are the results of two types of
stellar
explosions and are arranged in order of apparent age or
the time since light from the initial explosion first reached
planet Earth.
Clockwise starting at the upper left are remnants aged 600 years,
1,500 years, 10,000 years and 13,000 years.
The first three result from a
Type Ia
explosion - the destruction of a
white dwarf star by a thermonuclear
blast triggered by mass accreted from a stellar companion.
The fourth (lower left) is a
Type II
explosion - triggered by the final
collapse of the core of a massive star.
A neutron star, the remnant of the collapsed core,
lies at its center.
APOD: 2006 June 2 - IC 443: Supernova Remnant and Neutron Star
Explanation:
IC 443 is typical of the
aftermath
of a stellar explosion, the ultimate fate of massive stars.
Seen in this
false-color composite image, the
supernova remnant is still glowing
across the spectrum,
from radio (blue) to optical (red) to x-ray (green) energies --
even though light from the stellar
explosion that created the expanding cosmic cloud first
reached planet Earth thousands of years ago.
The odd thing about IC 443 is the apparent
motion of its dense
neutron star, the collapsed remnant of the
stellar core.
The close-up inset shows the swept-back wake created as the neutron star
hurtles
through the hot gas, but that direction
is not aligned with the direction toward the apparent center of
the remnant.
The misalignment suggests that the
explosion site was offset
from the center or that fast-moving gas in the nebula has
influenced the wake.
The wide view of IC 443, also known as the
Jellyfish nebula,
spans about 65 light-years at the supernova remnant's
estimated distance of 5,000 light-years.
APOD: 2006 May 19 - The Gum Nebula
Explanation:
Named for Australian astronomer
Colin Stanley
Gum (1924-1960),
The
Gum Nebula is so large and close
it is actually hard to see.
In fact, we are only about
450 light-years from the front edge
and 1,500 light-years from the back edge of this
cosmic cloud of glowing hydrogen gas.
Covered in
this 41 degree-wide
mosaic of H-alpha images, the faint
emission region is otherwise easy to lose against the
background of Milky Way stars.
The complex
nebula is thought to be a
supernova remnant over a million years old,
sprawling
across the southern constellations Vela and Puppis.
Sliding your cursor over this spectacular wide field view will
reveal the location of objects embedded in The Gum Nebula, including the
Vela supernova remnant.
APOD: 2006 April 30 - 1006 AD: Supernova in the Sky
Explanation:
A new star, likely the
brightest supernova in recorded
human history,
appeared in planet Earth's sky about 1,000 years ago today,
in 1006 AD.
The expanding debris cloud
from the stellar explosion
is still visible to modern
astronomers, but what did the supernova look like in 1006?
In celebration of the millennial anniversary of SN1006,
astronomer Tunc Tezel
offers this intriguing suggestion, based on a photograph
he took on February 22, 1998 from a site overlooking
the Mediterranean south of Antalya, Turkey.
On that date, bright Venus and a waning crescent Moon
shone in the early morning sky.
Adopting
calculations
which put the
supernova's
apparent brightness
between Venus and the crescent Moon,
he digitally superposed an appropriate new star in the picture.
He placed the star at the supernova's position in the
southerly constellation of Lupus
and used the water's reflection
of moonlight in the final image.
APOD: 2006 March 26 - Doomed Star Eta Carinae
Explanation:
Eta Carinae may be about to explode.
But no one knows when - it may be
next year, it may be one million years from now.
Eta Carinae's mass - about
100 times greater than our Sun -
makes it an excellent candidate for a full blown supernova.
Historical records do show that about 150 years ago Eta Carinae underwent an unusual outburst
that made it one of the brightest stars in the southern sky.
Eta Carinae, in the
Keyhole Nebula, is the only star currently
thought to emit natural LASER light.
This image, taken in 1996, resulted from sophisticated
image-processing procedures designed to bring out new details in the
unusual nebula that surrounds
this
rogue star.
Now clearly visible are two
distinct lobes, a hot central region, and strange radial streaks.
The lobes are filled with lanes of gas and
dust which absorb the blue and
ultraviolet light emitted near the center.
The streaks remain unexplained.
Will these clues tell us how the nebula was formed?
Will they better indicate when Eta Carinae will explode?
APOD: 2006 March 7 - A Nearby Supernova in Spiral Galaxy M100
Explanation:
One of the nearer supernovas of recent years was discovered
last month in the bright nearby galaxy
M100.
The supernova, dubbed
SN 2006X,
is still near its maximum brightness and visible with a telescope
toward the constellation of Berenice's Hair
(Coma Berenices)
The supernova,
pictured above, has been identified as
Type Ia indicating that a
white dwarf star in the
picturesque spiral galaxy has gone near its
Chandrasekhar limit
and exploded.
Although hundreds of supernovas are now discovered each year by automated searches,
nearby supernova are rare and important because they frequently become bright enough to be studied by many telescopes and are near enough for their immediate surroundings to be spatially resolved.
Supernova
2006X's host galaxy M100
resides in the
Virgo Cluster of Galaxies located about 50 million
light years from Earth.
APOD: 2007 February 17 - Supernova Remnant and Shock Wave
Explanation:
A
massive star ends
life as a supernova, blasting its outer layers back
to interstellar space.
The spectacular
death explosion is initiated by
the collapse of what has become an impossibly dense stellar core.
Pictured is
the expanding supernova remnant Puppis A -
one of the brightest sources in
the x-ray sky.
Now seen to be about 10 light-years in diameter, light from the
initial stellar explosion first reached Earth
a few thousand years ago.
Recorded by the
Chandra Observatory's
x-ray cameras, the inset view shows striking
details of
the strong shock wave disrupting an interstellar cloud
as the shock sweeps through preexisting material.
The larger field ROSAT image also captures a
pinpoint source of x-rays
near the remnant's center.
The source is a young
neutron star, the remnant of the
collapsed stellar core kicked out by the
explosion
and moving away at about 1,000 kilometers per second.
APOD: 2006 February 2 - Thor's Helmet in H-Alpha
Explanation:
Near picture center, the helmet-shaped structure with
wing-like appendages is popularly called
Thor's Helmet.
Cataloged as NGC 2359, the striking nebula is located about
15,000 light-years away in the constellation
Canis
Major.
The helmet is actually more like
a
cosmic bubble, blown as the
wind from the bright, massive star near the bubble's center sweeps
through the surrounding molecular cloud.
Known as a
Wolf-Rayet star, the energetic star is a blue giant
thought to be in a brief,
pre-supernova stage of evolution.
The remarkable color composite
combines broad and narrow band images -
including a deep exposure recorded with an
H-alpha filter.
The H-alpha image traces the light from
the region's glowing atomic hydrogen gas.
Heroically sized even for a
Norse god,
this Thor's Helmet is about 30 light-years across.
APOD: 2006 January 25 - The Expanding Light Echoes of SN 1987A
Explanation:
Can you find supernova 1987A?
It isn't hard -- it occurred at the center of the expanding
bullseye pattern.
Although this stellar detonation was first seen almost two decades ago,
light from it continues to bounce off clumps of
interstellar dust
and be reflected to us today.
These expanding
light echoes
have been recorded in the
above time-lapse movie recorded over four years from the
Blanco 4-meter telescope in
Chile.
The first image is an image of the
SN 1987A region,
while the next four images were created by subtracting consecutive images,
taken a year apart, and leaving only the difference between the images.
Light echoes can be seen moving out from the position of the supernova.
The SuperMACHO team who recorded the
above light echoes around
supernova 1987A
has also found faint and previously unnoticed
light echoes from two other
LMC supernovas.
Study of these light echoes
has enabled more accurate determinations of the location and date of these two
supernova explosions
that were first visible hundreds of years ago.
APOD: 2006 January 23 - The LMC Galaxy in Glowing Gas
Explanation:
What goes on inside of a galaxy?
To help find out, astronomers from the
Magellanic Cloud Emission Line Survey
team imaged our neighboring
LMC galaxy
in spectacular detail and highlighted very specific colors of
light emitted by glowing gas.
The above mosaic of over 1,500 images of the
Large Magellanic Cloud (LMC) is the result -- clicking on the image will bring up an
image with much greater detail.
The colors highlighted on the mosaic are light emitted by
hydrogen (red),
oxygen (green), and
sulfur (yellow), while light from individual stars has been subtracted.
The mosaic shows what a busy and violent place the inside of the LMC really is.
Visible in the above image are many small
planetary nebulas
pushed out by low mass stars, large
emission nebula of
ambient interstellar gas
set aglow by massive stars, and huge gaseous
supernova remnants cast off by massive stars
exploding.
The extended connected filaments are mostly connected supernova remnants.
The LMC,
a familiar sight to an unaided eye in the
southern hemisphere,
spans about 15,000 light years and lies only about 180,000
light years distant.
APOD: 2005 December 26 - SN 1006: Supernova Remnant in X Rays
Explanation:
This huge puff ball was once a star.
One thousand years ago, in the
year 1006, a
new star was recorded
in the sky that today we know was really an existing star exploding.
The resulting expanding gas from the
supernova
is still visible with telescopes today, continues to expand, and now spans over 70
light years.
SN 1006 glows in every type of light.
The above image of SN 1006 was captured by the orbiting
Chandra Observatory
in X-ray light.
Even today, not everything about the
SN 1006
is understood, for example why
particle shocks
that produce the bright blue filaments are only visible at some locations.
SN 1006 is thought to have once been a
white dwarf that exploded when gas being dumped onto it by its
binary star companion caused it to go over the
Chandrasekhar limit.
Foreground stars are visible that have nothing to do with the supernova.
APOD: 2005 December 6 - The Veil Nebula Unveiled
Explanation:
These wisps of gas are all that remain visible of a
Milky Way star.
Many thousands of years ago that star exploded in a
supernova leaving the
Veil Nebula,
pictured above.
At the time, the
expanding cloud
was likely as bright as a crescent
Moon toward the
constellation of
Cygnus,
visible for weeks to people living at the dawn of
recorded history.
The
supernova remnant lies about 1400
light-years away and covers over five times the size of the
full Moon.
The above image of the
Veil
was made clearer by digitally dimming stars in the frame.
The bright wisp at the top is known as the
Witch's Broom Nebula
and can be seen with a small telescope.
The Veil Nebula is also known as the
Cygnus Loop.
APOD: 2005 December 2 - Crab Nebula Mosaic from HST
Explanation:
The Crab Nebula is cataloged as M1, the first object on
Charles
Messier's famous list of things which are not comets.
In fact, the
cosmic Crab
is now known to be a
supernova remnant,
an expanding cloud of debris from the death explosion of a massive star.
Light from that stellar catastrophe was first
witnessed
by astronomers on planet Earth in the year 1054.
Composed of 24
exposures taken in October 1999, January 2000,
and December 2000, this
Hubble Space Telescope mosaic spans about twelve light years.
Colors in the intricate filaments trace the light emitted from atoms
of hydrogen, oxygen, and sulfur in the debris cloud.
The spooky blue interior glow is emitted by high-energy electrons
accelerated by the
Crab's central pulsar.
One of the most exotic objects known to modern astronomers,
the pulsar is
a neutron star, the spinning remnant of the
collapsed stellar core.
The Crab Nebula lies about 6,500 light-years away in the
constellation
Taurus.
APOD: 2005 November 29 - Simeis 147: Supernova Remnant from Palomar
Explanation:
It's easy to get lost following the intricate filaments in this
detailed
image of faint
supernova remnant Simeis 147.
Seen towards the constellation
Taurus
it covers nearly 3 degrees (6
full moons) on the sky corresponding to a width of 150 light-years at
the stellar debris cloud's estimated distance of 3,000 light-years.
The above image is a color composite of 66 blue and red color band images from the
National Geographic Palomar Observatory Sky Survey taken with the wide field
Samuel Oschin 48-inch Telescope.
The area of the sky shown covers over 70 times the area of the full Moon.
This supernova remnant has an apparent age of about 100,000
years - meaning light from the massive stellar explosion first
reached Earth 100,000 years ago - but this expanding remnant is not the only
aftermath.
The cosmic catastrophe also
left behind a spinning neutron star or pulsar, all that remains of the original star's core.
APOD: 2005 October 25 - Supernova Remnant N132D in Optical and X Rays
Explanation:
Thousands of years after a star exploded, its expanding remnant
still glows brightly across the spectrum.
Such is the case with
N132D, a
supernova remnant located in the neighboring
Large Magellanic Cloud (LMC) galaxy.
The expanding shell from this explosion now spans 80
light-years
and has swept up about 600 Suns worth of mass.
N132D was imaged recently in optical light and in great detail with the
Hubble Space Telescope.
The Hubble image was then combined with a position coincident detailed image in
X-ray light taken by the
Chandra X-ray Observatory.
The combination,
shown above
in representative colors, shows a nearly spherical expanding
shockwave
highlighted by pink emission from
hydrogen
gas and purple emission from
oxygen gas.
A dense field of unrelated stars also from the
LMC populates the image.
Studying the image gives an opportunity to study material
once hidden deep inside a star.
N132D spans about 150 light years and lies about 160,000
light years away toward the
constellation of
Dorado.
APOD: 2005 September 20 - M1: The Crab Nebula from NOT
Explanation:
This is the mess that is left when a star explodes.
The Crab Nebula, the result of a
supernova seen in
1054 AD,
is filled with mysterious filaments.
The filaments are not only
tremendously complex, but appear to have
less mass than expelled
in the original supernova and a
higher speed than expected
from a free explosion.
The above image, taken by the
Nordic Optical Telescope (NOT),
is in three colors chosen for scientific interest.
The Crab Nebula spans about 10 light-years.
In the nebula's very center lies a
pulsar: a
neutron star as massive as the
Sun
but with only the size of a
small town.
The Crab Pulsar
rotates about 30 times each second.
APOD: 2005 September 10 - Supernova Survivor
Explanation:
Beginning with a full view of beautiful spiral
galaxy M81,
follow the insets (left, bottom, then right) to
zoom in
on a real survivor.
Seen at the center of the final field on the right is a star
identified as the survivor of a cosmic cataclysm --
the supernova explosion of its companion star.
Light from the cosmic blast, likely triggered by the
core collapse of a star initially more than 10 times as massive as the Sun,
first reached Earth over 10 years ago and was
cataloged as
supernova SN 1993J.
Though the supernova itself is no longer visible,
light-echoes from
dust in the region can still be seen near the companion, the first
known survivor of a
supernova
in a binary star system.
Astronomers believe that a substantial
transfer of material
to the surviving companion star during the last few hundred years
before the stellar explosion can explain peculiarities seen
in this
supernova.
After supernova SN 1987A in the
Large Magellanic Cloud, SN 1993J
in nearby M81 is the brightest supernova seen in modern times.
APOD: 2005 August 13 - SNR 0103 72.6: Oxygen Supply
Explanation:
A supernova explosion,
a massive star's inevitable and
spectacular demise,
blasts back into space debris enriched in the
heavy elements
forged in its
stellar core.
Incorporated into future stars and planets, these are the
elements ultimately necessary for life.
Seen here in
a false-color x-ray image, supernova remnant
SNR 0103-72.6 is revealed to be just such an expanding debris
cloud in neighboring galaxy, the
Small Magellanic Cloud.
Judging from the measured size of the expanding outer ring of
shock-heated gas, about 150 light-years, light from
the original supernova explosion would have first reached
Earth about 10,000 years ago.
Hundreds of supernova remnants
have been identified as
much sought after astronomical laboratories for studying the cycle of
element synthesis
and enrichment, but the
x-ray data also show
that the hot gas at the center of this
particular supernova remnant is exceptionally rich
in neon and oxygen.
APOD: 2005 July 19 - A Nearby Supernova in M51
Explanation:
One of the nearest supernovas of recent years was
discovered late last month in the bright nearby galaxy
M51.
It is visible on the right of the
above before and after images of the
picturesque spiral.
Can you spot it?
The supernova, discovered originally by
Wolfgang Kloehr and now dubbed 2005cs,
is still near its maximum brightness and visible
with a telescope toward the constellation of the Hunting Dogs (Canes Venatici).
The supernova has been identified as a
Type II but has an unusual brightness history,
creating speculation that is similar in nature to the
brightest supernova of modern times:
1987A.
The progenitor star has been
identified as a bright blue star.
Although hundreds of supernovas are discovered each year by automated searches,
nearby supernova are rare and important because they frequently become bright enough to be studied by many telescopes and are near enough for their (former) host star and immediate surroundings to be spatially resolved.
Supernova 2005cs may have left behind a core that has been
compressed into a
neutron star or
black hole.
APOD: 2005 June 15 - Cassiopeia A Light Echoes in Infrared
Explanation:
Why is the image of Cassiopeia A changing?
Two images of the nearby supernova remnant taken a year apart in
infrared light
appear to show outward motions at tremendous speeds.
This was unexpected since the
supernova
that created the
picturesque nebula was seen 325 years ago.
The reason is likely light echoes.
Light from the supernova heated up distant ambient
dust that is just beginning to show its glow.
As time goes by, more distant dust
lights up,
giving the appearance of outward motion.
The
above image is a composite of
X-ray,
optical, and infrared light exposures that have been digitally combined.
The
infrared light image was taken by the orbiting
Spitzer
Space Telescope and was used in the discovery of the
light echo.
The portion of
Cassiopeia A
shown spans about 15
light years and lies 10,000 light years away toward the
constellation of
Cassiopeia.
APOD: 2005 June 8 - Rampaging Supernova Remnant N63A
Explanation:
What has this supernova left behind?
As little as 2,000 years ago, light from a massive stellar explosion in the
Large
Magellanic Cloud (LMC) first reached planet Earth.
The LMC is a close galactic neighbor of our
Milky Way Galaxy
and the rampaging
explosion
front is now seen moving out - destroying or displacing
ambient gas clouds while leaving behind relatively dense
knots of gas and dust.
What remains is one of the largest
supernova remnants in the
LMC: N63A.
Many of the surviving dense
knots have been themselves compressed and may further
contract to form new stars.
Some of the resulting stars may then explode in a supernova,
continuing the cycle.
Pictured above is a close-up of one of the largest
remaining knots of dust and gas in
N63A
taken by the orbiting Hubble Space Telescope.
N63A spans over 25
light years and lies about 150,000 light years away
toward the southern
constellation
of Dorado.
APOD: 2005 May 15 - On the Origin of Gold
Explanation:
Where did the
gold
in your jewelry originate?
No one is completely sure.
The relative average abundance in our
Solar System appears higher than can be made in the
early universe, in
stars, and even in typical
supernova explosions.
Some
astronomers
now suggest that neutron-rich heavy
elements such as
gold might be most easily
made in rare
neutron-rich
explosions such as the
collision of
neutron stars.
Pictured above is a computer-animated frame depicting two
neutron stars spiraling in toward each other,
just before they collide.
Since neutron star collisions are also suggested as the origin of
short
duration gamma-ray bursts,
it is possible that you already own a souvenir from one of the most
powerful explosions in the universe.
APOD: 2005 May 14 - NGC 3370: A Sharper View
Explanation:
Similar in size and grand design to our
own
Milky Way, spiral galaxy NGC 3370 lies about 100 million
light-years away toward the constellation Leo.
Recorded
here
in exquisite detail by the Hubble Space Telescope's
Advanced Camera for Surveys,
the big, beautiful face-on spiral does steal the show,
but the sharp image also reveals an impressive array of
background galaxies in the field, strewn across
the more distant Universe.
Looking within NGC 3370,
the
image data has proved sharp enough
to study individual pulsating stars known as
Cepheids which
can be used to accurately determine this galaxy's distance.
NGC 3370 was chosen for this study because in 1994
the spiral galaxy was also home to a well studied stellar
explosion -- a type Ia supernova.
Combining the known distance to this
standard candle supernova,
based on the Cepheid measurements, with observations
of supernovae at even greater distances,
can reveal the size and expansion rate of the
Universe
itself.
APOD: 2005 April 21 - G21.5-0.9: A Supernova's Cosmic Shell
Explanation:
The picture is lovely, but this
pretty
cosmic shell was
produced by almost unbelievable violence - created
when a star with nearly 20 times the mass
of the sun blasted away its outer layers in a spectacular
supernova explosion.
As the expanding debris cloud swept through surrounding interstellar
material, shock waves heated the gas causing the supernova remnant
to glow in x-rays.
In fact, it is possible that all supernova explosions create
similar shells,
some brighter than others.
Cataloged as G21.5-0.9, this
shell
supernova remnant is relatively faint,
requiring about 150 hours of x-ray data from the orbiting
Chandra
Observatory to create this false-color image.
G21.5-0.9 is about 20,000 light-years distant in the constellation
Scutum
and measures about 30 light-years across.
Based on the remnant's size, astronomers estimate that light
from the original stellar explosion
first
reached Earth several thousand years ago.
APOD: 2005 April 2 - Cyg X-1: Can Black Holes Form in the Dark?
Explanation:
The formation of a
black hole from the collapsing
core of a massive star is thought to be heralded by a spectacular
supernova explosion.
Such an extremely energetic collapse is also a
leading explanation
for the mysterious cosmic gamma-ray bursts.
But researchers now suggest that the Milky Way's most
famous black hole,
Cygnus X-1, was born
when a massive star collapsed --
without
any supernova explosion at all.
Their dynamical evidence is summarized in this
color image of a gorgeous
region in Cygnus,
showing Cyg X-1 and a cluster of massive stars
(yellow circles) known as Cygnus OB3.
Arrows compare the measured direction and speed of Cyg X-1
and the average direction and speed of the massive stars
of Cyg OB3.
The similar motions indicate that
Cyg X-1's progenitor star was itself a cluster member
and that its path was not altered at all when it
became a black hole.
In contrast, if Cyg X-1 were born in a violent supernova
it would have likely received a
fierce
kick, changing its course.
If not a supernova, could
the formation of the Cyg X-1 black
hole have produced a
dark gamma-ray burst in
the
Milky Way?
APOD: 2005 March 26 - Composite Crab
Explanation:
The Crab Pulsar, a city-sized, magnetized
neutron star
spinning 30 times a second,
lies at the center of this composite image of the inner region of
the well-known Crab
Nebula.
The spectacular picture combines optical data (red) from the
Hubble Space Telescope
and x-ray images (blue) from the
Chandra
Observatory, also used in the popular
Crab
Pulsar movies.
Like a
cosmic
dynamo the pulsar powers the x-ray
and optical emission from the nebula, accelerating
charged particles and producing the eerie, glowing x-ray jets.
Ring-like structures are x-ray emitting regions where
the high energy particles slam into the nebular material.
The innermost ring is about a light-year across.
With more mass than
the
Sun and the density of an
atomic nucleus,
the spinning pulsar is the collapsed core of a massive star
that exploded, while the nebula is the
expanding remnant of the star's outer layers.
The supernova explosion was witnessed in
the year 1054.
APOD: 2005 March 24 - Simeis 147: Supernova Remnant
Explanation:
It's easy to get lost following the intricate filaments in this
detailed
image of faint
supernova remnant Simeis 147.
Seen towards the constellation
Taurus
it covers nearly 3 degrees (6
full moons) on the sky corresponding to a width of 150 light-years at
the stellar debris cloud's estimated distance of 3,000 light-years.
The color composite image includes eight hours of exposure time
with an H-alpha filter, transmiting only
the light from recombining hydrogen atoms in the expanding
nebulosity and tracing the regions of
shocked, glowing gas.
This supernova remnant has an apparent age of about 100,000
years - meaning light from the massive stellar explosion first
reached Earth 100,000 years ago - but this expanding remnant is not the only
aftermath.
The cosmic catastrophe also left behind
a spinning neutron star or pulsar,
all
that remains of the original star's core.
APOD: 2004 December 23 - 3C58: Pulsar Power
Explanation:
Light from a star that exploded some ten thousand light-years
away first reached our fair planet in the year 1181.
Now known as supernova remnant 3C58, the region seen in
this false-color image glows in x-rays, powered by a rapidly
spinning
neutron star
or
pulsar - the dense
remains of the collapsed stellar core.
A cosmic dynamo with more mass than the sun, the pulsar's electromagnetic
fields seem to accelerate particles to enormous energies, creating
the jets, rings, and loop structures visible in this
stunning
x-ray view from the orbiting
Chandra
Observatory.
While adding 3C58 to the list of
pulsar
powered nebulae
explored with Chandra, astronomers
have deduced
that the pulsar itself is much too cool for its tender years,
citing 3C58 as a show case of extreme physics
not well understood.
The close-up inset above spans about six light-years.
APOD: 2004 December 16 - The Arms of NGC 7424
Explanation:
The grand, winding arms are almost mesmerizing in
this face-on view
of NGC 7424, a spiral galaxy with a prominent
central bar.
About 40 million light-years distant in the
headlong constellation
Grus, this island universe
is also about 100,000 light-years across making it remarkably
similar to our own
Milky Way.
Following along the winding arms, many bright
bluish clusters
of massive young stars can be found.
The star clusters themselves are several hundred light-years
in diameter.
And while massive stars are born in the arms of NGC 7424,
they also die there.
Notably, this galaxy was home to a
powerful stellar explosion,
supernova
SN 2001ig, which faded before this
deep European Southern Observatory image
was recorded.
APOD: 2004 November 28 - Doomed Star Eta Carinae
Explanation:
Eta Carinae may be about to explode.
But no one knows when - it may be
next year, it may be one million years from now.
Eta Carinae's mass - about
100 times greater than our Sun -
makes it an excellent candidate for a full blown supernova.
Historical records do show that about 150 years ago Eta Carinae underwent an unusual outburst
that made it one of the brightest stars in the southern sky.
Eta Carinae, in the
Keyhole Nebula, is the only star currently
thought to emit natural LASER light.
This image, taken in 1996, resulted from sophisticated
image-processing procedures designed to bring out new details in the
unusual nebula that surrounds
this
rogue star.
Now clearly visible are two
distinct lobes, a hot central region, and strange radial streaks.
The lobes are filled with lanes of gas and
dust which absorb the blue and
ultraviolet light emitted near the center.
The streaks remain unexplained.
Will these clues tell us how the nebula was formed?
Will they better indicate when Eta Carinae will explode?
APOD: 2004 November 5 - Supernova Remnant Imaged in Gamma Rays
Explanation:
Gamma rays are the most energetic
form of light.
With up to a billion times the energy of ordinary "medical"
x-rays,
they easily penetrate telescope lenses and mirrors, making it
very difficult to create
gamma-ray images of cosmic sources.
Still, an array of large telescopes
designed to detect gamma-ray
induced atmospheric flashes - the HESS
(High Energy
Stereoscopic System)
experiment - has produced this historic, resolved image of a
supernova remnant at extreme
gamma-ray energies.
Astronomers note that the
premier
gamma-ray view of the expanding
stellar debris cloud is clearly similar to x-ray images of the remnant
and convincingly supports the idea
that these sites of powerful
shock waves are also sources of cosmic
rays within our galaxy.
The gamma-ray intensity is color-coded in the picture, shown with
dark contour lines that trace levels of x-ray emission
from the object.
At an estimated distance of 3,000 light-years, the supernova
remnant measures about 50 light-years across and
lies near the galactic plane.
APOD: 2004 October 8 - Kepler's SNR from Chandra, Hubble, Spitzer
Explanation:
Light from the stellar explosion that
created this energized cosmic cloud was first seen on planet
Earth in October 1604, a mere
four hundred years
ago.
The supernova produced a bright
new star
in early 17th century skies within the constellation
Ophiuchus.
It was studied by astronomer
Johannes Kepler
and his contemporaries, with out the benefit of a telescope, as they
searched for an explanation of the heavenly apparition.
Armed with a
modern
understanding of stellar evolution,
early 21st century
astronomers continue to explore the
expanding debris cloud, but can now use
orbiting space telescopes to
survey Kepler's supernova remnant (SNR)
across the spectrum.
In this tantalizing composite image,
x-rays,
visible light, and
infrared
radiation recorded by NASA's astrophysical
observatories - the
Chandra X-Ray Observatory,
Hubble and
Spitzer
space telescopes - are combined to give a more comprehensive
view of the still enigmatic supernova remnant.
About 13,000 light years away,
Kepler's supernova
represents the most recent stellar explosion seen to
occur within
our Milky Way galaxy.
APOD: 2004 September 16 - Microquasar in Motion
Explanation:
Microquasars, bizarre binary star systems
generating high-energy radiation and blasting out jets of particles
at nearly the speed of light, live in our
Milky Way galaxy.
The energetic microquasar systems seem to consist of a very compact
object, either a neutron star or a black hole, formed in a supernova
explosion but still co-orbiting with
an otherwise normal star.
Using a very
long array of radio telescopes,
astronomers
are reporting
that at least one microquasar, LSI +61 303, can be
traced back
to its probable birthplace -- within a cluster of young stars
in the constellation Cassiopeia.
About 7,500 light-years from Earth, the star cluster and surrounding
nebulosity, IC 1805, are shown in the
deep sky image above.
The cluster stars are identified by yellow boxes and circles.
A yellow arrow indicates the common apparent motion of the
cluster stars, the green arrow shows the deduced sky motion of the
microquasar system, and the red arrow depicts the microquasar's
motion relative to the star cluster itself.
Seen nearly 130 light-years from the cluster it once called home,
a powerful kick from the original
supernova explosion likely set this
microquasar in motion.
APOD: 2004 September 7 - A Supernova in Nearby Galaxy NGC 2403
Explanation:
The closest and brightest supernova in over a decade was
recorded just over a month ago in the outskirts of
nearby galaxy NGC 2403.
Officially tagged
SN 2004dj, the
Type IIP
explosion likely annihilated most of a blue
supergiant star as central
fusion could no longer hold it up.
The supernova
can be seen as the bright object in the
above image in the direction of the arrow.
The home galaxy to the supernova, spiral galaxy
NGC 2403, is located only 11 million light years away and is visible with binoculars
toward the northern constellation of Camelopardalis (the Giraffe).
The supernova is fading but still visible with a telescope,
once peaking at just brighter than
magnitude 12.
Supernovas
of this type change brightness in a predictable way and may be
searched for in the
distant universe as distance indicators.
APOD: 2004 August 26- Cassiopeia A in a Million
Explanation:
One
million seconds of x-ray image data were used to construct
this view of supernova remnant Cassiopeia A,
the expanding debris cloud from a stellar explosion.
The stunningly detailed image from the
Chandra Observatory
will allow an unprecedented
exploration of the
catastrophic
fate that awaits stars much more massive
than the Sun.
Seen in false-color,
Cas A's outer green ring, 10 light-years
or so in diameter, marks the location of the expanding
shock from the original supernova explosion.
At about 10 o'clock around the ring, a structure
extends beyond it, evidence that the initial explosion
may have also produced energetic jets.
Still glowing in x-rays, the tiny point
source near the center of Cas A is a neutron star,
the collapsed remains of the stellar core.
While Cas A is about 10,000 light-years away, light from
the supernova explosion first
reached Earth just over
300 years ago.
APOD: 2004 May 22 - X-Rays From Tycho's Supernova Remnant
Explanation:
In 1572,
Danish
astronomer
Tycho Brahe
recorded the sudden appearance of
a bright new star in the constellation Cassiopeia.
The
new star faded from view over a period of months and is
believed to have been a supernova, one of the last stellar explosions
seen in our Milky Way galaxy.
Now known
as Tycho's Supernova Remnant, the expanding debris cloud is
shown in this detailed
false-color x-ray image
from the orbiting Chandra Observatory.
Represented in blue, the highest energy x-rays come from shocked regions
along the outer edges of the supernova remnant, corresponding to gas at
temperatures of 20 million degrees Celsius.
X-rays
from cooler gas (only 10 million degrees or so!) dominate the
remnant's interior.
Unlike some
other supernova remnants,
no hot central
point source
can be found, supporting the theory
that the origin of this stellar explosion
was a runaway nuclear detonation that ultimately
destroyed a white dwarf star.
At a distance of about 7,500 light-years,
Tycho's Supernova Remnant
appears to be nearly 20 light-years across.
This x-ray picture's field of view slightly cuts off the
bottom of the generally spherical cloud.
APOD: 2004 May 17 - NGC 3372: The Great Nebula in Carina
Explanation:
In one of the brightest parts of the
Milky Way
lies a nebula where some of the oddest things occur.
NGC 3372, known as the
Great Nebula in Carina,
is home to massive stars and changing nebula.
Eta Carina,
the most energetic star in the nebula was one of the
brightest stars in the sky in the 1830s,
but then faded dramatically.
The Keyhole Nebula, visible near the center,
houses several of the most massive stars
known and has also changed its appearance.
The Carina Nebula spans over 300 light years and
lies about 7000 light-years away in the constellation of Carina.
The above image was taken from La Frontera in Alcohuaz,
Chile.
Eta Carina
might explode in a dramatic
supernova
within the next thousand years, and has even
flared in brightness over just the
past decade.
APOD: 2004 April 29 - Titan's X-Ray
Explanation:
This June's rare and much heralded
transit of Venus will
feature our currently brilliant evening
star in silhouette,
as the inner planet glides across the face of the Sun.
But on January 5, 2003 an even rarer transit took place.
Titan, large moon
of ringed gas giant Saturn, crossed
in front of the Crab
Nebula, a supernova remnant some 7,000
light-years away.
During Titan's transit,
the orbiting Chandra Observatory's
x-ray detectors recorded the shadowing of cosmic x-rays generated
by the Crab's amazing pulsar
nebula, pictured above, in a situation analogous to a
medical
x-ray.
The resulting image (inset at left) probes the extent of
Titan's
atmosphere.
So, how rare was Titan's transit of the Crab?
While Saturn itself passes within a few degrees of the Crab
Nebula every 30 years, the next similar transit is reportedly
due in 2267.
And since the stellar explosion which gave birth to the Crab was
seen in 1054, the 2003 Titan transit may have been
the first to occur ... ever.
APOD: 2004 April 8 - Elusive Jellyfish Nebula
Explanation:
Normally faint and elusive, the Jellyfish Nebula is caught in
the net of
this spectacular wide-field telescopic view.
Flanked by two yellow-tinted stars at the foot of a
celestial
twin - Mu and
Eta
Geminorum -
the Jellyfish Nebula is the brighter arcing
ridge of emission with dangling tentacles just right of center.
Here, the cosmic jellyfish is seen to be
part of bubble-shaped
supernova remnant
IC 443, the expanding
debris cloud from an exploded star some 5,000 light-years away.
Also in view, emission nebula IC 444 nearly fills the field to
the upper left, dotted with small blue reflection nebulae.
Like its cousin in astrophysical waters, the
Crab Nebula,
IC 443 is known to harbor
a neutron star, the collapsed core of the massive star that
exploded over 30,000 years ago.
APOD: 2004 March 11 - Henize 206: Cosmic Generations
Explanation:
Peering into a dusty nebula in
nearby
galaxy the
Large Magellanic Cloud, infrared cameras on board the
Spitzer Space Telescope recorded
this detailed view of stellar
nursery Henize 206 filled with newborn stars.
The stars appear as white spots within the swirls of dust and gas
in the false-color infrared
image.
Near the top, the sweeping telltale arcs of a
supernova remnant
are also visible, expanding debris from the final explosion of
a massive star.
The proximity of the ancient supernova indicates that the shockwave from
that stellar death explosion itself likely
triggered the
formation of the new generation of emerging stars, compressing
the gas and dust within Henize 206 and continuing the
cosmic cycle
of star death and star birth.
At the distance of the Large
Magellanic Cloud, about 163,000
light-years, this image covers an area about 1,000 light-years across.
APOD: 2004 March 6 - N49's Cosmic Blast
Explanation:
Scattered debris from a cosmic supernova explosion
lights up the sky
in this gorgeous composited image based on data from the
Hubble Space Telescope.
Cataloged as N49, these glowing filaments of shocked gas
span about
30 light-years in our neighboring galaxy, the
Large Magellanic Cloud.
Light from the original exploding star reached Earth thousands
of years ago, but N49 also marks the location of another
energetic outburst -- an extremely intense
blast of gamma-rays
detected by satellites only twenty-five years ago on
March
5, 1979.
That date was the beginning of an
exciting journey in astrophysics
which led researchers to the understanding of an exotic new class of
stars.
The source of the March 5th Event is now attributed to
a
magnetar - a highly magnetized, spinning neutron star also
born in the ancient stellar explosion which created supernova
remnant N49.
The magnetar hurtles
through the supernova
debris cloud at over 1,200 kilometers
per second.
APOD: 2004 March 2 - NGC 6960: The Witch's Broom Nebula
Explanation:
Ten thousand years ago, before the dawn of recorded human history,
a new light must suddenly have appeared in the
night sky and faded after a few weeks.
Today we know this light was an exploding star and record the colorful expanding cloud as the
Veil Nebula.
Pictured above is the west end of the
Veil Nebula known technically as
NGC 6960 but less formally as the
Witch's
Broom Nebula.
The rampaging gas gains its colors by impacting and
exciting existing nearby gas.
The supernova remnant
lies about 1400 light-years away towards the constellation of
Cygnus.
This Witch's Broom actually spans over three times the
angular size of the full
Moon.
The bright star 52
Cygnus is visible with the unaided eye from
a dark location but unrelated to the ancient
supernova.
APOD: 2004 February 27 - Rumors of a Strange Universe
Explanation:
Only a few short years ago, when the
APOD editors were in graduate school,
the pervasive,
cosmic
Dark Energy was not even seriously discussed.
Of course, it now
appears that this strange energy dominates
the cosmos (as well as lectures
on
cosmology) and provides a
repulsive force accelerating the large scale
expansion of the Universe.
In fact, recent
brightness
measurements of distant and
therefore ancient, stellar explosions or supernovae
indicate that the universal expansion began to
speed up in earnest four to six billion years ago,
when the Dark Energy's repulsive force began to
overcome the attractive force of gravity over cosmic distances.
The
Hubble Space telescope images above show a sample of the
distant supernova explosions, billions of light-years away, in before
(top) and after (bottom) pictures of their faint host galaxies.
Hubble
measured supernovae also hint that the
Dark Energy's
repulsive force is constant over cosmic time and so could be
consistent with Einstein's
original theory of gravitation.
If the force actually changes with time, the Universe
could still end in a
Big Crunch or a
Big Rip ... but not for at least an
estimated 30 billion years.
APOD: 2004 February 20 - SN1987A's Cosmic Pearls
Explanation:
In February 1987, light from the brightest stellar explosion
seen in modern times reached Earth --
supernova SN1987A.
This Hubble Space Telescope
image from the sharp Advanced
Camera for Surveys taken in November 2003 shows
the explosion site over 16 years later.
The snap shot
indicates that the supernova blast wave
continues to impact a pre-existing, one light-year wide
ring of material, and the
nascent central supernova remnant
continues to expand.
Like pearls on a cosmic necklace, bright hot spots
produced as the
blast wave heats material up to millions of degrees began to appear
on the ring in the mid 1990s and have been followed
across the spectrum
by astronomers ever since.
Supernova SN1987A lies in the
Large Magellanic Cloud,
a neighboring galaxy some 170,000 light-years away.
That really does mean that the explosive event -
the core collapse and detonation of a star about 20 times as massive
as the Sun - occurred
170,000 years before February 1987.
APOD: 2004 February 12 - Supernova Survivor
Explanation:
Beginning with a full view of beautiful spiral
galaxy M81,
follow the insets (left, bottom, then right) to
zoom in
on a real survivor.
Seen at the center of the final field on the right is a star
recently identified as the survivor of a cosmic cataclysm --
the supernova explosion of its companion star.
Light from the cosmic blast, likely triggered by the
core collapse of a star initially more than 10 times as massive as the Sun,
first reached Earth over 10 years ago and was
cataloged as
supernova SN 1993J.
Though the supernova itself is no longer visible,
light-echoes from
dust in the region can still be seen near the companion, the first
known survivor of a
supernova
in a binary star system.
Astronomers believe that a substantial
transfer of material
to the surviving companion star during the last few hundred years
before the stellar explosion can explain peculiarities seen
in this
supernova.
After supernova SN 1987A in the
Large Magellanic Cloud, SN 1993J
in nearby M81 is the brightest supernova seen in modern times.
APOD: 2004 January 28 - The Crab Nebula from CFHT
Explanation:
This is the mess that is left when a star explodes.
The Crab Nebula, the result of a
supernova seen in
1054 AD,
is filled with mysterious filaments.
The filaments are not only
tremendously complex, but appear to have
less mass than expelled
in the original supernova and a
higher speed than expected
from a free explosion.
The above image, taken by the
Canada-France-Hawaii Telescope (CFHT),
is in three colors chosen for scientific interest.
The Crab Nebula spans about 10 light-years.
In the nebula's very center lies a
pulsar: a
neutron star as massive as the
Sun
but with only the size of a
small town.
The Crab Pulsar
rotates about 30 times each second.
APOD: 2004 January 1 - Structure in N63A
Explanation:
Shells and arcs abound in this false-color,
multiwavelength view of
supernova
remnant N63A, the debris of
a massive stellar explosion.
The x-ray emission
(blue), is from gas heated to 10 million degrees C as knots of
fast moving material from
the
cosmic blast sweep up
surrounding interstellar matter.
Radio (red) and optical emission (green)
are brighter near the central regions where the x-rays
seem to be absorbed by denser, cooler material on the side of
the expanding debris cloud facing the Earth.
Located in the neighboring galaxy known as the
Large Magellanic Cloud,
the apparent
age
of this supernova remnant is between 2,000 and 5,000 years,
its extended glow spanning about 60 light-years.
The intriguing image is a
composite of x-ray data from the orbiting
Chandra
Observatory, optical data from the
Hubble Space Telescope, and
radio from the
Australia Telescope Compact Array.
APOD: 2003 November 3 - Spiral Galaxy NGC 3982 Before Supernova
Explanation:
What do stars look like just before they explode?
To find out, astronomers
are taking detailed images of nearby galaxies now,
before any supernova is visible.
Hopefully, a star in one of the hundreds of
high resolution galaxy images
will explode in the coming years.
If so, archival images like that taken above by the
Hubble Space Telescope
can be inspected to find what the star looked like originally.
This information is likely important for better understanding
of how and why supernovas occur, as well as why some
supernovas appear brighter than others.
Pictured above, beautiful
spiral galaxy NGC 3982 displays numerous
spiral arms filled with bright stars,
blue star clusters, and dark
dust lanes.
NGC 3982, which spans about 30,000 light years, lies about 60 million
light years from
Earth and can be seen with a small telescope toward the
constellation of
Ursa Major.
APOD: 2003 October 16 - NGC 6888: X-Rays in the Wind
Explanation:
NGC 6888, also known as
the Crescent Nebula, is
a cosmic bubble of interstellar gas about 25 light-years across.
Created by
winds from the bright, massive star seen near the center
of this composite image, the
shocked filaments of gas glowing at optical
wavelengths are represented in green and yellowish hues.
X-ray
image data from a portion of the nebula viewed by
the Chandra Observatory is overlaid in blue.
Such isolated
stellar wind
bubbles are not usually seen to
produce
energetic x-rays, which require
heating gas to a million degrees celsius.
Still, NGC 6888 seems to have accomplished this
as slow moving winds from the central star's initial transition
to a red supergiant
were overtaken and rammed by faster
winds driven by the intense radiation from the star's
exposed inner layers.
Burning fuel
at a prodigious rate and near the end
of its stellar life, NGC 6888's central star
should ultimately go out with a bang, creating a supernova
explosion in 100,000 years or so.
NGC 6888 is about 5,000 light-years close, toward the constellation
Cygnus.
APOD: 2003 September 26 - IC1340 in the Eastern Veil
Explanation:
These ghostly filaments of interstellar gas are just a small
part of the
expansive
Veil Nebula, seen against a rich field
of background stars in the
long-necked
constellation
Cygnus.
Also known as the
Cygnus Loop, the Veil Nebula is a
supernova remnant,
the expanding debris cloud created by a stellar
explosion whose light first reached planet Earth
from 5,000 to 10,000 years ago.
About 1,400 light-years away,
the entire nebula now appears
to span over 3 degrees on
the sky, nearly 6 times the apparent size of the full moon,
but is faint and can be difficult to see in small telescopes.
The region captured in
this
beautiful, deep, color image
is located at the southern tip of the Veil's
eastern
crescent.
It covers about 10 light-years at the distance of
the Veil and is cataloged as IC1340.
APOD: 2003 September 14 - The Crab Nebula from VLT
Explanation:
The Crab Nebula, filled with mysterious filaments, is the result of a
star that was seen to explode in 1054 AD.
This spectacular supernova explosion was recorded by Chinese and (quite probably) Anasazi Indian astronomers.
The filaments are mysterious because they appear
to have less mass than expelled in the original supernova
and higher speed than expected from a free explosion.
In the above picture taken recently from a
Very Large Telescope,
the color indicates what is happening to the
electrons in differentparts of the
Crab Nebula.
Red indicates the electrons are recombining with protons to form neutral hydrogen,
while blue indicates the electrons are whirling around the magnetic field
of the inner nebula.
In the
nebula's very center lies a pulsar: a neutron star rotating, in this case, 30 times a second.
APOD: 2003 September 11 - NGC 3370: A Sharper View
Explanation:
Similar in size and grand design to our
own
Milky Way, spiral galaxy NGC 3370 lies about 100 million
light-years away toward the constellation Leo.
Recorded
here
in exquisite detail by the Hubble Space Telescope's
Advanced Camera for Surveys,
the big, beautiful face-on spiral does steal the show,
but the sharp image also reveals an impressive array of
background galaxies in the field, strewn across
the more distant Universe.
Looking within NGC 3370,
the
image data has proved sharp enough
to study individual pulsating stars known as
Cepheids which
can be used to accurately determine this galaxy's distance.
NGC 3370 was chosen for this study because in 1994
the spiral galaxy was also home to a well studied stellar
explosion -- a type Ia supernova.
Combining the known distance to this
standard candle supernova,
based on the Cepheid measurements, with observations
of supernovae at even greater distances,
can reveal the size and expansion rate of the
Universe
itself.
APOD: 2003 September 4 - Composite Crab
Explanation:
The Crab Pulsar, a city-sized, magnetized
neutron star
spinning 30 times a second,
lies at the center of this composite image of the inner region of
the well-known Crab
Nebula.
The spectacular picture combines optical data (red) from the
Hubble Space Telescope
and x-ray images (blue) from the
Chandra
Observatory, also used in the popular
Crab
Pulsar movies.
Like a
cosmic
dynamo the pulsar powers the x-ray
and optical emission from the nebula, accelerating
charged particles and producing the eerie, glowing x-ray jets.
Ring-like structures are x-ray emitting regions where
the high energy particles slam into the nebular material.
The innermost ring is about a light-year across.
With more mass than
the
Sun and the density of an
atomic nucleus,
the spinning pulsar is the collapsed core of a massive star
that exploded, while the nebula is the
expanding remnant of the star's outer layers.
The supernova explosion was witnessed in
the year 1054.
APOD: 2003 September 3 - Galactic Supernova Remnant IC 443
Explanation:
About 8000 years ago, a star in
our Galaxy exploded.
Ancient humans might have noticed the
supernova as a temporary star, but
modern humans can see the expanding shell of gas even today.
Pictured above, part of the shell of
IC 443 is seen to be composed of
complex filaments,
some of which are impacting an existing
molecular cloud.
Here emission from
shock-excited
molecular
hydrogen is allowing astronomers to study how fast moving
supernova gas affects star formation in the cloud.
Additionally, astronomers theorize that the
impact accelerates some particles to velocities near the speed of light.
Supernova remnant
IC 443 is also known to shine brightly also in
infrared and
X-ray light.
APOD: 2003 August 30 - Recycling Cassiopeia A
Explanation:
For billions of years,
massive stars in our Milky Way
Galaxy have lived spectacular lives.
Collapsing from vast cosmic
clouds, their nuclear furnaces
ignite and create heavy elements in their cores.
After a few million years, the
enriched material is blasted
back into interstellar space where star formation
begins anew.
The expanding debris cloud known
as
Cassiopeia A is an example
of this final phase of the stellar life cycle.
Light from the explosion which created this supernova remnant was
probably first
seen
in planet Earth's sky just over 300 years ago,
although it took that light more than 10,000 years to reach us.
In this gorgeous
Hubble Space Telescope image of cooling filaments
and knots in the Cas A remnant, light
from specific elements has been color coded to help astronomers
understand the recycling of our galaxy's
star stuff.
For instance, red regions are dominated by emission from sulfur atoms
while blue shades correspond to oxygen.
The
area shown is about 10 light-years across.
APOD: 2003 August 23 - The Tarantula Zone
Explanation:
The
Tarantula Nebula is more than 1,000 light-years across -
a giant emission nebula within our
neighboring galaxy
the Large Magellanic Cloud.
Inside this cosmic arachnid lies a central young cluster of massive
stars, cataloged as
R136, whose intense radiation and strong winds
have helped energize the nebular glow and shape the spidery filaments.
In this
impressive color mosaic
of images from the
Wide-Field Imager
camera on ESO's 2.2 meter telescope at La Silla Observatory, other
young star clusters can be seen still within the
nebula's grasp.
Also notable among the denizens
of the Tarantula zone are several
dark clouds
invading the nebula's outer limits as well as
the dense cluster
of stars NGC 2100 at the extreme left edge of the
picture.
The small but expanding remnant of
supernova 1987a, the closest supernova
in modern history,
lies just off the lower right corner of the field.
The rich mosaic's field of view covers an area on the sky
about the size of
the full moon in the southern
constellation Dorado.
APOD: 2003 July 4 - N49's Cosmic Blast
Explanation:
Scattered debris from a cosmic supernova explosion
lights up the sky
in this gorgeous composited image based on data from the
Hubble Space Telescope.
Cataloged as N49, these glowing filaments of shocked gas
span about
30 light-years in our neighboring galaxy, the
Large Magellanic Cloud.
Light from the original exploding star reached Earth thousands
of years ago, but N49 also marks the location of another
energetic outburst -- an extremely intense
blast of gamma-rays
detected by satellites on
March
5, 1979.
That date was the beginning of an
exciting journey in astrophysics
which led researchers to the understanding of an exotic new class of
stars.
The source of the "March 5th Event" is now attributed to
a
magnetar - a highly magnetized, spinning neutron star also
born in the ancient stellar explosion which created supernova
remnant N49.
The magnetar hurtles
through the supernova
debris cloud at over 1,200 kilometers
per second.
APOD: 2003 June 12 - Cyg X-1: Can Black Holes Form in the Dark?
Explanation:
The formation of a
black hole from the collapsing
core of a massive star is thought to be heralded by a spectacular
supernova explosion.
Such an extremely energetic collapse is also a
leading explanation
for the mysterious cosmic gamma-ray bursts.
But researchers now suggest that the Milky Way's most
famous black hole,
Cygnus X-1, was born when a massive
star collapsed --
without
any supernova explosion at all.
Their dynamical evidence is summarized in this
color image of a gorgeous
region in Cygnus,
showing Cyg X-1 and a cluster of massive stars
(yellow circles) known as Cygnus OB3.
Arrows compare the measured direction and speed of Cyg X-1
and the average direction and speed of the massive stars
of Cyg OB3.
The similar motions indicate that
Cyg X-1's progenitor star was itself a cluster member
and that its path was not altered at all when it
became a black hole.
In contrast, if Cyg X-1 were born in a violent supernova
it would have likely received a
fierce
kick, changing its course.
If not a supernova, could
the formation
of the Cyg X-1 black
hole have produced a dark
gamma-ray burst in
the
Milky Way?
APOD: 2003 June 9 - The Pencil Nebula Supernova Shockwave
Explanation:
At 500,000 kilometers per hour, a
supernova
shockwave plows through interstellar space.
This shockwave is known as the
Pencil Nebula, or NGC 2736, and is part of the
Vela supernova remnant,
an expanding shell of a star that exploded about
11,000 years ago.
Initially the shockwave was moving at millions of kilometers
per hour, but the weight of all the gas it has
swept up has slowed it considerably.
Pictured above, the
shockwave moves from left to right,
as can be discerned by the lack of gas on the left.
The above region spans nearly a
light year across, a
small part of the 100+ light-year span of the entire
Vela supernova remnant.
The Hubble Space Telscope
ACS captured the
above image last October.
APOD: 2003 May 28 - SNR 0103-72.6: Oxygen Supply
Explanation:
A supernova explosion,
a massive star's inevitable and
spectacular demise,
blasts back into space debris enriched in the heavy elements
forged
in its
stellar core.
Incorporated into future stars and planets, these are the
elements ultimately necessary for life.
Seen here in
a false-color x-ray image, supernova remnant
SNR 0103-72.6 is revealed to be just such an expanding debris
cloud in neighboring galaxy, the
Small
Magellanic Cloud.
Judging from the measured size of the expanding outer ring of
shock-heated gas, about 150 light-years, light from
the original supernova explosion would have first reached
Earth about 10,000 years ago.
Hundreds of supernova remnants
have been identified as
much sought after astronomical laboratories for studying the
cycle of
element synthesis
and enrichment, but the
x-ray data also show
that the hot gas at the center of this
particular supernova remnant is exceptionally rich
in neon and oxygen.
APOD: 2003 May 3 - Denizen of the Tarantula Nebula
Explanation:
The star cluster at lower right,
cataloged
as Hodge 301, is a denizen of
the Tarantula Nebula.
An evocative nebula in the southern sky,
the sprawling cosmic Tarantula is an energetic
star
forming region some 168,000 light-years distant
in our neighboring galaxy the Large Magellanic Cloud.
The stars within Hodge 301 formed together tens of millions of years ago
and as the massive ones quickly exhaust their nuclear fuel they
explode.
In fact, the giant stars of
Hodge 301
are rapidly approaching this violent final phase of stellar evolution -
known
as a supernova.
These supernova blasts send material and
shock
waves back into the nebular
gas to create the Tarantula's glowing filaments also visible in this
Hubble Space Telescope
Heritage image.
But these spectacular stellar death explosions signal star birth
as well, as the blast waves condense gas and dust to ultimately
form the next generation of stars
inside the Tarantula Nebula.
APOD: 2003 April 20 - The Gum Nebula Supernova Remnant
Explanation:
Because the Gum Nebula is the closest
supernova remnant,
it is actually hard to see.
Spanning 40
degrees across the sky, the nebula is so
large and faint
it is easily lost in the
din of a bright and complex background.
The Gum Nebula, highlighted nicely in the
above wide angle photograph,
is so close that we are
much nearer the front edge than the back edge,
each measuring 450 and 1500
light years respectively.
The
complex nebula lies in the direction of the
constellations of Puppis and Vela.
Oddly, much remains unknown about the Gum Nebula, including the
timing and even number of supernova explosions that formed it.
APOD: 2003 April 14 - A Gamma Ray Burst Supernova Connection
Explanation:
New evidence has emerged that a mysterious type of
explosion known as a gamma ray burst
is indeed connected to a supernova of the type visible in the
above image.
Two weeks ago, the orbiting
HETE satellite
detected gamma-ray burst
GRB030329.
The extremely bright burst was
found hours later
to have an extremely bright
afterglow in
visible light, and soon set the record for the closest measured distance at
redshift 0.17.
The afterglow
brightness allows
unprecedented coverage
of its evolution.
Just this week, as many astronomers suspected would happen,
the afterglow began to appear as a fading
Type II Supernova.
Type II Supernovas might not appear coincident with
gamma-ray bursts, however,
when the gamma-ray beam goes in another direction.
The above spiral galaxy,
NGC 3184, was home to a
Type II Supernova in 1999 at the position of the arrow.
Astronomers are currently pressing
hard to find the host galaxy
for GRB030329.
APOD: 2003 March 28 - 1006 AD: Supernova in the Sky
Explanation:
A new star, likely the
brightest supernova in recorded
human history,
appeared in planet Earth's sky in the year 1006 AD.
The expanding debris cloud
from the stellar explosion is still
visible to modern astronomers, but what did the supernova look
like in 1006?
Astronomer
Tunç Tezel
offers this suggestion, based on a photograph
he took on February 22, 1998 from a site overlooking
the Mediterranean south of Antalya, Turkey.
On that date, bright Venus and a waning crescent Moon
shone in the early morning sky.
Adopting
recent
calculations which put the supernova's apparent
brightness between Venus and the crescent Moon,
he digitally superposed an appropriate new star in the picture.
He placed the star at the supernova's position in the
southerly constellation of Lupus
and used the water's reflection
of moonlight in the final image.
Tezel hopes to view the total solar eclipse of
29
March 2006 from
this same site -- on the 1,000th anniversary of
Supernova
1006.
APOD: 2003 March 17 - SN 1006: History's Brightest Supernova
Explanation:
Suddenly, in the year 1006 AD, a
new star appeared in the sky.
Over the course of just a few days, the rogue star
became brighter than the planet
Venus.
The star, likely the talk of everyone who could see it,
was recorded by people who lived in areas now known as
China,
Egypt,
Iraq,
Italy,
Japan, and Switzerland.
The celestial newcomer, now known to be a
supernova,
took months to fade.
Modern observations have been used to measure the speed of the
still-expanding shock wave,
allowing a better estimate of its
distance and hence a better estimate of the
true brightness of the
supernova.
It turns out
SN 1006 likely achieved an apparent visual
magnitude of -7.5, making it the brightest
supernova on record.
The shock wave was imaged in 1998 from
CTIO
(left panel), and then subtracted from a similar
image taken in 1986 (right panel), highlighting the
relative expansion.
APOD: 2003 March 14 - DEM L71: When Small Stars Explode
Explanation:
Large, massive stars
end their furious lives in spectacular
supernova
explosions -- but small, low mass stars may encounter a similar fate.
In fact, instead of simply cooling off
and quietly fading away,
some white dwarf stars in binary star systems
are thought to draw enough mass
from their companions to
become unstable, triggering a
nuclear detonation.
The resulting standard candle stellar explosion is classified as
a Type Ia supernova
and perhaps the best example yet of the aftermath
is this expanding cloud of shocked stellar debris, DEM L71, in
the nearby
Large Magellanic Cloud.
The sharp false-color
x-ray
image from the orbiting
Chandra
Observatory shows the predicted bright edges of the outer
blast wave shock region and
the x-ray glow of an inner region of reverse shock heated gas.
Based on
the Chandra data, estimates for the composition
and total mass of expanding gas
strongly suggest that this is all that remains of a white dwarf star.
Light from this small star's self-destructive explosion would have
first reached Earth several thousand years ago.
APOD: 2003 February 4 - Wisps of the Veil Nebula
Explanation:
These wisps of gas are all that remain visible of a
Milky Way star.
Many thousands of years ago that star exploded in a
supernova leaving the
Veil Nebula,
pictured above. At the time, the
expanding cloud
was likely as bright as a crescent
Moon toward the
constellation of
Cygnus,
visible for weeks to people living at the dawn of
recorded history.
The remaining
supernova remnant lies about 1400
light-years away and covers over five times the size of the
full Moon.
The bright wisp on the right is known as the
Witch's Broom Nebula
and can be seen with a small telescope.
The Veil Nebula is also known as the
Cygnus Loop.
APOD: 2003 January 18 - Filaments in the Cygnus Loop
Explanation:
Subtle and delicate in appearance, these are filaments of shocked
interstellar gas -- part of the expanding
blast wave from a violent stellar explosion.
Recorded in November 1997 with the
Wide Field and Planetary Camera 2
on board the Hubble Space Telescope,
the picture is
a closeup of a supernova remnant known as
the Cygnus Loop.
The nearly edge-on view shows a small portion of the
immense shock front
moving toward the top of the frame at about 170 kilometers per second
while glowing in light emitted
by atoms of excited hydrogen gas.
Not just another pretty picture, this particular image has
provided some
dramatic
scientific results.
In 1999, researchers used it to substantially revise downward
widely accepted estimates of distance and age for this classic
supernova remnant.
Now determined to lie only 1,440 light-years away, the
Cygnus Loop is
thought to have been expanding for 5 - 10 thousand years.
APOD: 2003 January 1 - NGC 6960: The Witch's Broom Nebula
Explanation:
Ten thousand years ago, before the dawn of recorded human history,
a new light must suddenly have appeared in the
night sky and faded after a few weeks.
Today we know this light was an exploding star and record the colorful expanding cloud as the
Veil Nebula.
Pictured above is the west end of the
Veil Nebula known technically as
NGC 6960
but less formally as the Witch's Broom Nebula.
The rampaging gas gains its colors by impacting and
exciting existing nearby gas.
The supernova remnant
lies about 1400 light-years away towards the constellation of
Cygnus.
This Witch's Broom actually spans over three times the
angular size of the full
Moon.
The bright blue star 52
Cygnus is visible with the unaided eye from
a dark location but unrelated to the ancient
supernova.
APOD: 2002 December 27 - X Ray Mystery in RCW 38
Explanation:
A mere 6,000 light-years distant and sailing through the constellation
Vela,
star cluster RCW 38
is full of powerful stars.
It's no surprise that these stars,
only a million years young with hot outer atmospheres,
appear as
point-like x-ray sources dotting
this
x-ray image from the orbiting
Chandra
Observatory.
But the diffuse cloud of x-rays surrounding them is a bit
mysterious.
The image is color coded by x-ray energy, with high energies
in blue, medium in green, and low energy x-rays in red.
Just a few light-years across, the cloud
which pervades the cluster has colors suggesting
the x-rays
are produced by high energy electrons
moving
through magnetic fields.
Yet a source of energetic electrons, such as shockwaves
from exploding stars (supernova remnants),
or rotating neutron stars
(pulsars), is not apparent in the Chandra data.
Whatever their origins, the energetic particles could leave an imprint on
planetary systems forming in young star cluster RCW 38, just
as nearby energetic
events seem to have affected the chemistry and
isotopes found in our own solar system.
APOD: 2002 September 12 - X-Rays From Tycho's Supernova Remnant
Explanation:
In 1572,
Danish
astronomer
Tycho Brahe
recorded the sudden appearance of
a bright new star in the constellation Cassiopeia.
The
new star faded from view over a period of months and is
believed to have been a supernova, one of the last
stellar explosions seen
in our Milky Way galaxy.
Now known
as Tycho's Supernova Remnant, the expanding debris cloud is
shown in this detailed
false-color x-ray image
from the orbiting Chandra Observatory.
Represented in blue, the highest energy x-rays come from shocked regions
along the outer edges of the supernova remnant, corresponding to gas at
temperatures of 20 million degrees Celsius.
X-rays
from cooler gas (only 10 million degrees or so!) dominate the
remnant's interior.
Unlike some
other supernova remnants,
no hot central
point source
can be found, supporting the theory
that the origin of this
stellar explosion
was a runaway nuclear detonation that ultimately
destroyed a white dwarf star.
At a distance of about 7,500 light-years,
Tycho's Supernova Remnant
appears to be nearly 20 light-years across.
This x-ray picture's field of view slightly cuts off the
bottom of the generally spherical cloud.
APOD: 2002 August 30 - Simeis 147: Supernova Remnant
Explanation:
It's easy to get lost following the intricate filaments in this
stunningly
detailed image of faint
supernova remnant Simeis 147.
Seen towards the constellation Taurus
it covers nearly 3 degrees (6
full moons) on the sky corresponding to a width of 150 light-years at
the stellar debris cloud's estimated distance of 3,000 light-years.
On three separate nights in December 2001 and January 2002
astronomer
Steve Mandel accumulated a total of over eight hours of exposure time to
compose this image.
He used an astronomical CCD camera, telephoto lens,
and his specially designed adapter to allow such
wide-field
digital imaging.
He also used a narrow H-alpha
filter to transmit only the
the light from recombining hydrogen atoms in the expanding
nebulosity, defining the regions of
shocked, glowing gas.
This supernova remnant has an apparent age of about 100,000 years
(light from the original explosion first reached Earth 100,000 years
ago) but it is not the only
aftermath of the massive stellar explosion.
The cosmic catastrophe also left behind
a spinning neutron star or pulsar,
all
that remains of the star's dense core.
APOD: 2002 August 24 - Cas A Supernova Remnant in X Rays
Explanation:
The complex shell of a star seen to explode
300 years ago is helping astronomers to
understand how that star exploded.
This
Chandra Observatory image of supernova remnant
Cassiopeia A (Cas A) shows unprecedented detail in three
x-ray colors.
The relationship between brightness, color,
and position of material in the image indicates
where in the star this material was just before
the explosion.
Bright knots on the left, for example, contain little iron,
and so are hypothesized to originate from a higher layer
than outer red filaments, which are iron rich.
The blue region on the right is seen through absorbing
dust,
and so appears depleted of low-energy x-rays.
It takes light ten years to cross the gas shell of the
Cas A supernova remnant, which is 10,000
light-years distant.
Most of the
elements
that make people and planets were produced in
supernova explosions.
APOD: 2002 July 14 - The Crab Nebula from VLT
Explanation:
The Crab Nebula, filled with mysterious filaments, is the result of a
star that was seen to explode in 1054 AD.
This spectacular supernova explosion was recorded by Chinese and (quite probably) Anasazi Indian astronomers.
The filaments are mysterious because they appear
to have less mass than expelled in the original supernova
and higher speed than expected from a free explosion.
In the above picture taken recently from a
Very Large Telescope,
the color indicates what is happening to the electrons in different
parts of the Crab Nebula.
Red indicates the electrons are recombining with protons to form neutral hydrogen,
while blue indicates the electrons are whirling around the magnetic field
of the inner nebula.
In the
nebula's very center lies a pulsar: a neutron star rotating, in this case, 30 times a second.
APOD: 2002 July 12 - Recycling Cassiopeia A
Explanation:
For billions of years,
massive stars in our Milky Way
Galaxy have lived spectacular lives.
Collapsing from vast cosmic
clouds, their nuclear furnaces
ignite and create heavy elements in their cores.
After a few million years, the
enriched material is blasted
back into interstellar space where star formation
begins anew.
The expanding debris cloud known
as
Cassiopeia A is an example
of this final phase of the stellar life cycle.
Light from the explosion which created this supernova remnant was
probably first
seen
in planet Earth's sky just over 300 years ago,
although it took that light more than 10,000 years to reach us.
In this gorgeous
Hubble Space Telescope image of cooling filaments
and knots in the Cas A remnant, light
from specific elements has been color coded to help astronomers
understand the recycling of our galaxy's
star stuff.
For instance, red regions are dominated by emission from sulfur atoms
while blue shades correspond to oxygen.
The
area shown is about 10 light-years across.
APOD: 2002 June 13 - The Tarantula Zone
Explanation:
The
Tarantula Nebula is more than 1,000 light-years across -
a giant emission nebula within our neighboring galaxy
the Large Magellanic Cloud.
Inside this cosmic arachnid lies a central young cluster of massive
stars, cataloged as
R136, whose intense radiation and strong winds
have helped energize the nebular glow and shape the spidery filaments.
In this
impressive color mosaic
of images from the
Wide-Field Imager
camera on ESO's 2.2 meter telescope at La Silla Observatory, other
young star clusters can be seen still within the
nebula's grasp.
Also notable among the denizens
of the Tarantula zone are several
dark clouds
invading the nebula's outer limits as well as
the dense cluster
of stars NGC 2100 at the extreme left edge of the
picture.
The small but expanding remnant of
supernova 1987a, the closest supernova
in modern history,
lies just off the lower right corner of the field.
The rich mosaic's field of view covers an area on the sky
about the size of
the full moon in the southern
constellation Dorado.
APOD: 2002 May 23 - N132D and the Color of X-Rays
Explanation:
Supernova remnant N132D shows off complex structures in
this
sharp, color x-ray image.
Still, overall this
cosmic debris from a massive
star's explosive death has a strikingly simple horseshoe shape.
While N132D
lies 180,000 light-years distant in the
Large Magellanic Cloud,
the expanding remnant
appears here about 80 light-years across.
Light from the
supernova blast which created it would have reached
planet Earth about 3,000 years ago.
Observed by the orbiting
Chandra
Observatory, N132D still glows in
x-rays, its shocked gas heated
to millions of degrees
Celsius.
Since x-rays are invisible,
the Chandra x-ray image data are represented
in this picture by
assigning visible
colors to
x-rays with
different energies.
Low energy x-rays are shown as red, medium energy as green, and
high energy as blue colors.
These color choices make a pleasing picture and they also
show the x-rays in the same energy order as
visible light photons, which range
from low to high energies as red, green, and blue.
APOD: 2002 May 17 - Gamma Ray Burst, Supernova Bump
Explanation:
On the 21st of November 2001,
satellites
detected yet another
burst of gamma-rays from the cosmos.
While this flash of high-energy
photons lasted for less than a minute,
eager astronomers
have been following the
fading
optical light from the
location of the burst source ever since.
Seen above
in a series of Hubble Space Telescope images
recorded from December 4, 2001 to May 5, 2002 (13 through 161 days
after the burst), the fading transient lies to the right of a
fuzzy, distant galaxy, likely home
to the gamma-ray burster.
Two constant point-like objects to the left of the galaxy are foreground
stars within our own Milky Way.
The transient did not not simply fade away, though.
Observations from the Hubble,
OGLE, and the large
Magellan telescope
in Chile indicate that it bumped up or brightened again days after
the burst in a convincing display
characteristic
of a supernova - the
death explosion of a massive star.
These results
add to the mounting
evidence that at least
some of the mysterious cosmic
gamma-ray
bursts are produced in the
violent event
which ends the lives of massive stars.
APOD: 2002 April 28 - Doomed Star Eta Carinae
Explanation:
Eta Carinae may be about to explode.
But no one knows when - it may be
next year, it may be one million years from now.
Eta Carinae's mass - about
100 times greater than our Sun -
makes it an excellent candidate for a full blown supernova.
Historical records do show that about 150 years
ago Eta Carinae underwent an unusual outburst
that made it one of the brightest stars in the
southern sky.
Eta Carinae, in the
Keyhole Nebula, is
the only star currently
thought to emit natural LASER light.
This image, taken in 1996, resulted from sophisticated
image-processing procedures designed to bring out new details in the
unusual nebula that surrounds
this
rogue star.
Now clearly visible are two
distinct lobes, a hot central region, and strange radial streaks.
The lobes are filled with lanes of gas and
dust which absorb the blue and
ultraviolet light emitted near the center.
The streaks remain unexplained.
Will these clues tell us how the nebula was formed?
Will they better indicate when Eta Carinae will explode?
APOD: 2002 April 5 - Gamma Ray Burst Afterglow: Supernova Connection
Explanation:
What causes the mysterious
gamma-ray bursts?
Indicated in this
Hubble Space Telescope exposure of an otherwise
unremarkable field in the constellation
Crater, is the dwindling
optical afterglow of a gamma-ray burst first
detected
by the Beppo-SAX satellite on 2001 December 11.
The burst's host galaxy,
billions of light-years distant, is the
faint smudge extending above and to the left of the afterglow position.
After rapidly catching the
fading
x-ray light from the burst with
the orbiting XMM-Newton
observatory, astronomers are
now reporting
the telltale signatures of
elements
magnesium, silicon,
sulphur, argon, and calcium - material most likely found in an
expanding debris
cloud produced by the explosion of a massive star.
The exciting result
is evidence that the gamma-ray burst itself
is linked to a very energetic supernova
explosion
which may have
preceded the powerful
flash of gamma-rays by up to a few days.
APOD: 2002 March 31 - The Mysterious Rings of Supernova 1987A
Explanation:
What's causing those odd rings in
supernova 1987A?
In 1987, the brightestsupernova
in recent history occurred in the
Large Magellanic Clouds.
At the
center of the picture is an object central to the remains of the violent
stellar explosion. When the
Hubble Space Telescope was pointed at the
supernova remnant
in 1994, however, the existence of
curious
rings was
confirmed.
The
origins of these rings still remains a mystery. Speculation into the cause
of the rings includes
beamed jets emanating from a dense star left over
from the supernova, and a
superposition of two stellar winds ionized by the
supernova explosion.
APOD: 2002 February 28 - ESO 184-G82: Supernova - Gamma Ray Burst Connection
Explanation:
Modern astronomers keep a long list of things that go bump
in the night.
Near the top are supernovae - the death
explosions of massive stars, and
gamma-ray bursts - the most powerful
explosions seen
across the Universe.
Intriguingly,
the galaxy in the above
Hubble Space Telescope
image may have been host to both a supernova and a gamma-ray burst
which were one and the same event.
ESO 184-G82 is a spiral galaxy with a prominent
central bar
and loose spiral arms dotted with bright star-forming regions.
The inset shows an expanded view
of one of the star-forming regions, about 300 light-years across.
Indicated is the location of an
extraordinarily powerful supernova explosion
whose light first reached planet Earth on April 25, 1998.
That location and date also correspond to the detection of an
unusual
gamma-ray burst,
which may be representative of a peculiar
class of
these cosmic high-energy flashes.
So far, this combination is unique and makes barred spiral
ESO 184-G82,
at a distance of only 100 million light-years,
the closest known gamma-ray burst host galaxy.
APOD: 2002 February 23 - Shocked by Supernova 1987A
Explanation:
Fifteen years ago today, the
brightest supernova of modern times
was sighted.
Over time,
astronomers have watched and waited for
the expanding debris from this tremendous stellar
explosion to crash into
previously expelled material.
A clear result of such a collision is demonstrated above
in two frames
recorded by the Hubble Space Telescope in 1994 (left)
and 1997(right).
While the central concentration of
stellar
debris has clearly evolved over this period,
the yellow spot on the ring in the righthand
picture announces the collision of an outward
moving
blast wave with the pre-existing, light-year wide ring.
The collision is occurring at speeds near
60 million kilometers per hour and
shock-heats the
ring material causing it to glow.
Astronomers are hopeful that such collisions will
illuminate the interesting past of
SN 1987A, and perhaps provide more clues
about the origin of the mysterious rings.
APOD: 2002 February 18 - A Radio Vista of Cygnus
Explanation:
Shells of ancient
supernovas, cocoons surrounding
newborn stars, and specks from
distant quasars highlight this
tremendous vista toward the constellation of
Cygnus.
The representative color image covers about 10 degrees
across on the sky but is only a small part of the
Canadian Galactic Plane Survey in
radio light.
Diffuse bands of
ionized gas flow though a dominating region of
star formation, located about 6000
light-years away.
Two prominent
supernova shells visible include the brown globule on the lower left and the white bumpy sphere on the upper right.
To the left of the brown globule is the entire
North America Nebula.
Prominent stellar cocoons
are visible throughout the image as bright white knots.
Some of these stars will likely generate future
supernova shells.
Far in the distance, visible here as only red dots,
quasars glow.
APOD: 2001 December 27 - The Incredible Expanding Crab
Explanation:
The Crab Nebula is cataloged as M1, the first on
Charles Messier's
famous list of things which are not comets.
In fact, the Crab is
now known to be a supernova remnant, an expanding
cloud of debris from the explosion of a massive star.
The violent birth of the Crab was
witnessed
by astronomers in the year 1054.
Roughly 10 light-years across today, the nebula is still expanding
at a rate of over 1,000 kilometers per second.
Flipping between two images made nearly 30 years apart, this
animation clearly demonstrates the expansion.
The smaller Crab was recorded as a
photographic image made in 1973
using the Kitt Peak
National Observatory 4-meter telescope in 1973.
The
expanded Crab was made this year with the Kitt Peak
Visitor Center's
0.4-meter telescope and digital camera.
Background stars were used to register the two images.
APOD: 2001 December 2 - Rumors of a Strange Universe
Explanation:
Three years ago
results were
first presented indicating that
most of the energy in our universe is not in
stars or galaxies but is tied to space itself.
In the language of cosmologists, a large
cosmological constant is directly implied by new distant
supernovae observations.
Suggestions of a
cosmological constant (lambda) are
not new -- they have existed since the advent of
modern relativistic cosmology.
Such claims are
not usually popular with astronomers, though, because lambda is so unlike known universe components, because
lambda's value appears limited by other observations,
and because less-strange cosmologies without lambda have
previously done well in explaining the data.
What is noteworthy here is the seemingly direct and reliable method of the observations and the good reputations of the
scientists conducting
the investigations.
Over the past three years, two independent
teams of astronomers have continued to accumulate data
that appears to confirm the unsettling result.
The
above picture of a supernova that occurred in
1994
on the outskirts of a
spiral galaxy
was taken by one of these collaborations.
Still,
extraordinary claims require extraordinary evidence,
and so cosmologists the world over continue to await
more data and confirmation by independent methods.
APOD: 2001 October 27 - Sher 25: A Pending Supernova
Explanation:
No supernova
has ever been predicted.
These dramatic stellar explosions
that destroy stars and disperse elements
that compose
people and
planets
are not so well understood that astronomers can accurately
predict when a star will explode - yet.
Perhaps Sher
25 will be the first.
Sher 25, designated by the arrow, is a blue
supergiant
star located just outside the star cluster and emission nebula
NGC 3603.
Sher 25 lies in the center of an
hourglass shaped nebula much like the
one that surrounds the last bright supernova visible from Earth:
SN1987a.
Now the hourglass shaped rings around
SN1987a
were emitted before that blue supergiant exploded.
Maybe Sher 25 has expelled these bipolar rings in a step
that closely precedes a supernova.
If so, Sher 25 may be within
a few thousand years of its spectacular finale.
APOD: 2001 October 26 - Elements in the Aftermath
Explanation:
Massive stars
spend their brief
lives furiously burning nuclear fuel.
Through fusion
at extreme temperatures and densities surrounding the
stellar core, nuclei of light elements
like Hydrogen
and Helium are combined to heavier
elements like
Carbon, Oxygen, etc. in a progression which ends with Iron.
And so a supernova explosion,
a massive star's inevitable and spectacular demise,
blasts back into space debris
enriched in
heavier elements to be incorporated into other stars and planets (and
people!).
This detailed
false-color x-ray image
from the orbiting Chandra
Observatory shows such a hot, expanding stellar
debris
cloud about 36 light-years across.
Cataloged as G292.0+1.8, this young supernova remnant
in the southern constellation
Centaurus resulted from
a massive star which exploded an estimated 1,600 years ago.
Bluish colors highlight filaments of the mulitmillion degree gas
which are exceptionally
rich in Oxygen, Neon, and Magnesium.
Just below and left of center, a point like object in the Chandra image
suggests that
the
enriching supernova also produced a pulsar in
its aftermath, a rotating neutron star remnant of the collapsed stellar
core.
APOD: 2001 September 28 - NGC 6992: A Glimpse of the Veil
Explanation:
After 5,000 years, the gorgeous
Veil
Nebula is still turning heads.
Cataloged as NGC 6992, these glowing
filaments of interstellar
shocked gas are part of a larger spherical
supernova remnant known as the
Cygnus Loop or the
Veil Nebula -- expanding debris from a star which
exploded over 5,000 years ago.
This color digital image of a
bit
of the Veil has been processed
and enhanced to reveal stunning details in the diaphanous cosmic cloud.
Seen from our perspective against a rich Milky Way star field,
the Veil Nebula is
now
known to lie some 1,400 light-years away toward the
constellation Cygnus.
At that distance,
witnesses
to the original stellar explosion would have
seen a star in the heavens
increase in brightness to about -8 magnitude, roughly corresponding to
the brightness of the crescent Moon.
APOD: 2001 July 19 - Pulsar Wind in the Vela Nebula
Explanation:
The Vela pulsar was born
10,000 years ago at the center of
a supernova -- an
exploding star.
In this Chandra Observatory
x-ray image, the pulsar still produces a
glowing nebula at the heart of the expanding cloud of
stellar debris.
The pulsar
itself is a
neutron star,
formed as the stellar core
was compacted to nuclear densities.
With a strong magnetic field, approximately the mass of the Sun,
and a diameter of about 20 kilometers, the Vela pulsar rotates
11 times a second.
The sharp Chandra image
aids astronomers
in understanding
such extreme systems as efficient
high-voltage
generators
which drive structured winds
of electrically charged particles.
An x-ray bright nebula is created as the pulsar winds
slam into the surrounding material.
This view spans about 6 light-years across the central region of the
much larger Vela supernova remnant.
APOD: 2001 July 12 - NGC 1850: Not Found in the Milky Way
Explanation:
A mere 168,000 light-years distant, this large, lovely cluster of
stars, NGC 1850,
is located near the outskirts of the central
bar structure in our neighboring galaxy, the
Large
Magellanic Cloud.
A first glance
at
this Hubble Space Telescope
composite
image suggests that
this cluster's size and shape are reminiscent of the ancient globular
star clusters which roam our own
Milky Way Galaxy's halo.
But NGC 1850's stars are young ... making it a type
of star cluster
with no known counterpart
in the Milky Way.
NGC 1850 is also a double star cluster, with a second, compact
cluster of stars visible here below and to the right of
the large cluster's central region.
Stars in the large cluster are estimated to be
50 million
years
young, while stars in the compact cluster are
younger still, with an age of about 4 million years.
In fact, the smaller cluster
contains T-Tauri
stars, thought
to be low mass, solar-type stars still
in the
process of formation.
The glowing nebula at the left, like the
supernova remnants in our own galaxy,
testifies to violent stellar explosions,
indicating short-lived massive stars
were also present
in NGC 1850.
APOD: 2001 June 23 - The Cygnus Loop
Explanation:
The shockwave from a 20,000 year-old
supernova explosion
in the constellation of Cygnus
is still expanding into interstellar space.
The collision of this fast moving wall of gas with
a stationary cloud has heated it causing it to
glow in visible as well as
high energy radiation, producing the nebula known as the
Cygnus Loop (NGC 6960/95).
The nebula is located a mere 1,400 light-years
away.
The colors used here indicate emission from
different kinds of atoms excited by the
shock:
oxygen-blue, sulfur-red, and hydrogen-green.
This picture was taken with
the Wide Field and Planetary Camera 2 on board the
Hubble Space Telescope.
APOD: 2001 June 2 - The Pulsar Powered Crab
Explanation:
In the Summer of 1054 A.D.
Chinese astronomers reported
that a star in the
constellation of Taurus suddenly became as bright as the full Moon.
Fading slowly, it remained visible for over a year.
It is now understood
that a spectacular supernova explosion -
the detonation of a massive star whose remains
are now visible as the Crab Nebula-
was responsible for the apparition.
The
core of the star collapsed to form a rotating
neutron
star or
pulsar,
one of the most exotic objects known to modern astronomers.
Like a cosmic lighthouse, the rotating Crab pulsar generates beams of
radio, visible, x-ray and
gamma-ray energy which, as the name
suggests, produce pulses as they sweep across our view.
Using a stunning series of
visible
light images taken with
the Hubble Space Telescope (HST) in 1995, astronomers have discovered
spectacular pulsar powered motions within the Crab nebula.
Highlights of this
HST Crab "movie" show wisps of material moving
away from the pulsar at half the speed of light, a scintillating halo,
and an intense knot of emission dancing, sprite-like, above the pulsar's pole.
Only 10 kilometers wide but more
massive than the sun, the pulsar's energy drives the dynamics and emission
of the nebula itself which is more than 10 light-years across.
APOD: 2001 April 4 - Distant Supernova, Dark Energy
Explanation:
A pinpoint of light from a star that exploded over
10 billion light-years away
is centered in the panel at the lower right,
a cosmic
snapshot of the most
distant supernova.
The ancient stellar detonation
was detected
by digitally subtracting before and
after images of a faint, yellowish, elliptical galaxy
included in the Hubble Space Telescope Deep
Field image illustrated at the top and left.
Remarkable in itself as the
farthest known supernova, its measured
brightness provides astounding
evidence for
a strange universe -
one which eventually
defies gravity and expands at an
accelerating rate.
The unseen force driving
this
expansion is attributed to
"dark energy"
and discovering the fundamental
nature
of dark energy has been called
the challenge of this millennium.
APOD: 2001 March 25 - The Crab Nebula from VLT
Explanation:
The Crab Nebula, filled with mysterious filaments, is the result of a
star that was seen to explode in 1054 AD.
This spectacular supernova explosion was recorded by Chinese and (quite probably) Anasazi Indian astronomers.
The filaments are mysterious because they appear
to have less mass than expelled in the original supernova
and higher speed than expected from a free explosion.
In the above picture taken recently from a
Very Large Telescope,
the color indicates what is happening to the electrons in different
parts of the Crab Nebula.
Red indicates the electrons are recombining with protons to form neutral hydrogen,
while blue indicates the electrons are whirling around the magnetic field
of the inner nebula.
In the
nebula's very center lies a pulsar: a neutron star rotating, in this case, 30 times a second.
APOD: 2000 December 24 - NGC 1850: Gas Clouds and Star Clusters
Explanation:
There's nothing like it in
our own Galaxy.
Globular clusters as young as
NGC 1850 don't exist here.
Globular clusters
only 40 millions of years old
can still be found in the neighboring
LMC galaxy,
though, but perhaps none so unusual as
NGC 1850.
Close inspection of the
above photograph will reveal two clusters.
Below and right of the main group of stars known as
NGC 1850A is a smaller, still younger group dubbed
NGC 1850B.
This cluster is made of stars
only about four million years old.
The large red cloud of gas surrounding the
clusters may have been predominantly created by
supernovae explosions of stars in the younger cluster.
The red
supernova remnant
N57D is visible on the upper left.
APOD: 2000 December 15 - IC443's Neutron Star
Explanation:
Using
x-ray data from the orbiting
Chandra Observatory
along with radio data from the
Very Large Array,
a team of researchers has
discovered evidence for
a new example of one of the most bizarre objects known to
modern astrophysics -- a
neutron star.
Embedded within
supernova remnant IC443,
the suspected neutron star
appears as the reddish source at the lower right
in this false-color x-ray image.
Perhaps 20 kilometers across but with more mass than the Sun,
this ultracompact object is the collapsed core of a massive
star.
The core collapsed when the star, located a reassuring
5,000 light-years away
in the constellation
Gemini, exploded long ago.
How long ago?
Judging from the characteristic
bow wave shape of the
x-ray nebula
the researchers have estimated the speed of the neutron
star as it plows away from the explosion site.
Comparing the speed to the measured distance traveled from
the center of IC443,
the team,
three high school students and a teacher from the
North Carolina School for Science and Mathematics,
calculated that the light from the supernova
explosion arrived at Earth about 30,000 years ago.
APOD: 2000 December 2 - SN 1006: Pieces of the Cosmic Ray Puzzle
Explanation:
Research
balloon flights
conducted in 1912 by Austrian physicist Victor Hess
revealed that the Earth was constantly bombarded by high energy
radiation from space - which
came to be called "Cosmic Rays".
What are Cosmic Rays and where do they come from?
They are now known to be mostly subatomic particles - predominantly
protons and electrons -
but their origin is a long standing mystery.
After almost a century of study,
this cosmic puzzle may have been at least partially solved by
X-ray images
and spectra from the
ASCA satellite observatory.
Pieced together to show the region around a star observed to go
supernova in 1006 AD, the overlapping X-ray snapshots above
(seen in false color) reveal the bright rims of
the exploded star's still expanding
blast wave.
These ASCA observations showed for the
first time that the energy spectrum of the bright regions is like that
produced by extremely high energy electrons
streaming through a magnetic field at nearly the speed of light.
If (as expected) high energy protons are associated with
these energetic electrons
then supernova remnants like SN 1006 are sources of Hess'
puzzling Cosmic Rays.
APOD: 2000 November 7 - The Gum Nebula Supernova Remnant
Explanation: Because the Gum Nebula is the closest
supernova remnant,
it is actually hard to see.
Spanning 40
degrees across the sky, the nebula is so
large and faint
it is easily lost in the
din of a bright and complex background.
The Gum Nebula, highlighted nicely in the
above wide angle photograph,
is so close that we are
much nearer the front edge than the back edge,
each measuring 450 and 1500
light years respectively.
The
complex nebula lies in the direction of the constellations of Puppis and Vela.
Oddly, much remains unknown about the Gum Nebula, including the
timing and even number of supernova explosions that formed it.
APOD: 2000 August 23 - NGC 6960: The Witch's Broom Nebula
Explanation:
Ten thousand years ago, before the dawn of recorded human history,
a new light must suddenly have appeared in the
night sky and faded after a few weeks.
Today we know this light was an exploding star and record the colorful expanding cloud as the
Veil Nebula.
Pictured above is the west end of the
Veil Nebula known technically as
NGC 6960
but less formally as the Witch's Broom Nebula.
The rampaging gas gains its colors by impacting and
exciting existing nearby gas.
The
supernova remnant lies about
1400 light-years away towards the constellation of
Cygnus.
This Witch's Broom actually spans over three times the
angular size of the full
Moon.
The bright blue star 52
Cygnus is visible with the unaided eye from
a dark location but unrelated to the ancient
supernova.
APOD: 2000 August 13 - Doomed Star Eta Carinae
Explanation:
Eta Carinae may be about to explode.
But no one knows when - it may be
next year, it may be one million years from now.
Eta Carinae's mass - about
100 times greater than our Sun -
makes it an excellent candidate for a full blown supernova.
Historical records do show that about 150 years
ago Eta Carinae underwent an unusual outburst
that made it one of the brightest stars in the
southern sky.
Eta Carinae, in the
Keyhole Nebula, is
the only star currently
thought to emit natural LASER light.
This image, taken in 1996, resulted from sophisticated
image-processing procedures designed to bring out new details in the
unusual nebula that surrounds
this
rogue star.
Now clearly visible are two
distinct lobes, a hot central region, and strange radial streaks.
The lobes are filled with lanes of gas and
dust which absorb the blue and
ultraviolet light emitted near the center.
The streaks remain unexplained.
Will these clues tell us how the nebula was formed?
Will they better indicate when Eta Carinae will explode?
APOD: 2000 July 11 - The Crab Nebula in Blue and White
Explanation:
The Crab Nebula is a complex shell of expanding gas.
The
Crab Nebula formed from a
star that was seen to explode in a
supernova about 1000 years ago.
This two color composite image taken with the
WIYN 3.5-meter telescope shows in great
detail filamentary structure of the glowing
hydrogen gas.
Also known as
M1, the center is home to a dense
neutron star, a star as massive as our
Sun but only the size of a
city.
The
neutron star is a
pulsar that spins thirty times a second and spits out
energy that powers the nebula.
The
nebula
is named from its likeness to a
crab in an early drawing.
The
Crab Nebula still
presents mysteries today as the total mass of the
nebula and
pulsar appears much less than the mass of the original
pre-supernova star!
APOD: 2000 June 9 - Vela Pulsar: Neutron Star-Ring-Jet
Explanation:
This
stunning image from the orbiting
Chandra X-ray
Observatory is centered on the Vela pulsar -- the collapsed
stellar core within
the Vela supernova remnant
some 800 light-years distant.
The Vela pulsar is a
neutron star.
More massive than the Sun, it has the density of an atomic nucleus.
About 12 miles in diameter it
spins 10 times a second as it hurtles through the
supernova debris cloud.
The pulsar's electric and magnetic fields accelerate
particles to nearly the speed of light, powering the compact
x-ray emission nebula revealed
in the Chandra picture.
The cosmic crossbow shape is over 0.2 light-years across,
composed of an arrow-like jet emanating from the polar region of
the
neutron star and bow-like inner and outer arcs believed
to be the edges of tilted rings of x-ray
emitting high energy particles.
Impressively, the swept back compact nebula indicates the
neutron star is moving up and to the right in this
picture, exactly along the direction of the x-ray jet.
The Vela pulsar (and
associated
supernova remnant) was created by a massive
star which exploded over 10,000 years ago.
Its awesome x-ray rings and jet are reminiscent of another
well-known pulsar powered system,
the Crab Nebula.
APOD: 2000 May 12 - X-Ray Ring Around SN1987A
Explanation:
This
false-color image from the
Chandra X-ray Observatory
reveals a one light-year diameter ring of hot, ten million degree plasma.
It is one of the most detailed
X-ray images of the
expanding blast wave from
supernova 1987A
(SN1987A).
At visible wavelengths
SN1987A
is famous for its evolving rings, and
superposed on this image are white contour lines which outline the
innermost optical ring as seen by the
Hubble Space Telescope.
The composite picture clearly shows that the X-ray emitting shocked
material lies just inside the optical ring.
In fact,
the X-ray
emission seems to peak (whitest color) close to
where the optical emission peaks (closely spaced contours), a persuasive
demonstration that the optical light
is produced as the blast wave plows into surrounding material.
What will
SN1987A look like in the future?
According to a popular model,
in coming years the expanding supernova blast wave should
hit and light up even more material while
the violent impacts send reverse
shocks back towards
the site of the explosion and light up the ejected stellar debris.
In any event, astronomers will watch eagerly from a ringside seat as a
new supernova remnant emerges.
APOD: 2000 April 26 - Filaments In The Cygnus Loop
Explanation:
Subtle and delicate in appearance, these are filaments of shocked
interstellar gas -- part of the expanding
blast wave from a violent stellar explosion.
Recorded in November 1997 with the
Wide Field
and Planetary Camera 2
onboard the Hubble Space Telescope,
the picture is
a closeup of a supernova remnant known as
the Cygnus Loop.
The nearly edge-on view shows a small portion of the
immense shock front
moving toward the top of the frame at about 170 kilometers per second
while glowing in light emitted by atoms of
excited Hydrogen gas.
Not just another pretty picture, this particular image has
provided some
dramatic
scientific results.
In 1999, researchers used it to substantially revise downward
widely accepted estimates of distance and age for this classic
supernova remnant.
Now determined to lie only 1,440 light-years away, the
Cygnus Loop is
thought to have been expanding for 5 - 10 thousand years.
APOD: 2000 April 21 - M82: Starburst in X-rays
Explanation:
Star formation occurs at a faster pace
in M82
-- a galaxy with about 10 times the rate of massive star birth (and
death) compared to our Milky Way.
Winds from massive stars and blasts from supernova explosions
have created the expanding
cloud of million degree gas filling the above
Chandra X-ray Observatory image of this
remarkable
starburst galaxy.
The false color image even resolves bright spots which are likely
shocked supernova remnants and
X-ray bright
binary stars.
Also observed
as a radio
galaxy and a bright celestial infrared source,
M82's
aspect in optical pictures has led to its popular
moniker, the Cigar Galaxy.
M82's burst of star formation was likely triggered a mere
100 million years ago in the latest of a
series of bouts
with another large galaxy, M81.
APOD: 2000 April 14 - Supernova Remnant E0102 72 from Radio to X-Ray
Explanation:
Not all stars form a big Q after they explode.
The shape of
supernova remnant
E0102-72, however,
is giving astronomers a clue about how
tremendous explosions disperse
elements
and interact with surrounded gas.
The
above image is a composite of three
different photographs in three different
types of light.
Radio waves, shown in red, trace high-energy
electrons spiraling around
magnetic field lines in the
shock wave expanding out from the detonated star.
Optical light, shown in green, traces clumps of
relatively cool gas that includes oxygen.
X-rays, shown in blue, show relatively
hot gas that has been heated to millions of
degrees.
This gas has been heated by an inward moving
shock wave that has rebounded from a collision
with existing or slower moving gas.
This big Q currently measures 40
light-years across and was found
in our neighboring
SMC galaxy.
Perhaps we would know even more if we could
buy a vowel.
APOD: 2000 March 12 - Supernova 1994D and the Unexpected Universe
Explanation:
Far away, long ago, a star exploded.
Supernova 1994D, visible as the bright spot on the lower left,
occurred in the outskirts of disk galaxy NGC 4526.
Supernova 1994D was not of interest for how different it was,
but rather for how similar it was to other supernovae.
In fact, the light emitted during the
weeks after its explosion caused it to be given
the familiar designation of a Type Ia supernova.
If all Type 1a supernovae have the same intrinsic brightness,
then the dimmer a supernova appears, the farther away it must be.
By calibrating a precise
brightness-distance relation,
astronomers are able to estimate not only the
expansion rate of the universe (parameterized by the
Hubble Constant),
but also the
geometry of the universe we live in
(parameterized by
Omega and
Lambda).
The large number and great distances to supernovae measured over the past few years
have been interpreted
as indicating that we live in a
previously unexpected universe.
APOD: 2000 February 17 - New Shocks For Supernova 1987A
Explanation:
In February of 1987, astronomers witnessed the brightest
supernova
of modern times -
supernova 1987A in the
Large Magellanic Cloud.
Mysterious rings of material
surrounding the
expanding stellar debris
were soon emitting a visible glow excited by intense
light from the explosion.
After fading over the intervening years, the interior ring
has just been seen to
sprout four new hotspots, as illustrated in
these two versions of a
Hubble Space Telescope image recorded
on February 2nd.
The abrupt appearance of the new features suggests that
matter from the stellar blast wave itself has begun to
slam into the ring in earnest, shock-heating the gas and producing
the bright hotspots.
The left-hand picture shows the glowing ring, initially excited
by light from the explosion, along with the
shocked hotspots.
The right-hand picture has been further computer enhanced
to emphasize the hotspots.
The brightest spot at the right
was first observed in 1997, while the
four spots on the left half of the ring are new.
Astronomers now eagerly anticipate a dramatic
rejuvenation
of the glowing ring as the bulk of the blast wave material,
traveling at about 60 million kilometers per hour,
continues to plow into it.
APOD: 2000 February 11 - XMM-Newton First Light: X-Rays From The LMC
Explanation:
Recently the European Space Agency released this and other
spectacular "first light" pictures from its new
orbiting x-ray observatory, christened
XMM-Newton.
A churning region of star birth and death
in our small neighboring galaxy, the
Large Magellanic Cloud (LMC),
this field was one of several
chosen to test out XMM-Newton's
x-ray imaging capabilities.
The picture is a false-colour one in which low energy x-rays
are translated to red, medium energy to green, and high energy
to blue.
Image colours therefore
represent the relative million degree
temperatures of the x-ray emitting regions, red being the coolest
and blue the hottest.
Remains of the star that exploded as
Supernova 1987a appear here
as the white x-ray source at the lower right, while another
supernova remnant,
cataloged as N157D is the brightest
source at the upper left.
The bluish arc (near center) also appears to be a
supernova remnant whose
expanding debris cloud is interacting with
the LMC's local interstellar gas.
APOD: 2000 February 6 - The Mysterious Rings of Supernova 1987A
Explanation:
What's causing those odd rings in
supernova 1987A?
In 1987, the brightest
supernova
in recent history occurred in the
Large Magellanic Clouds. At the
center of the picture is an object central to the remains of the violent
stellar explosion. When the
Hubble Space Telescope was pointed at the
supernova remnant
in 1994, however, the existence of
curious
rings was
confirmed.
The
origins of these rings still remains a mystery. Speculation into the cause
of the rings includes
beamed jets emanating from a dense star left over
from the supernova, and a
superposition of two stellar winds ionized by the
supernova explosion.
Meanwhile, astronomers have just reported the possible appearance of a
new
ring feature.
APOD: 2000 January 3 - Cas A Supernova Remnant in X-Rays
Explanation:
The complex shell of a star seen to explode
300 years ago is helping astronomers to
understand how that star exploded.
The above recently released image of supernova remnant
Cassiopeia A (Cas A) shows unprecedented detail in three
X-ray colors.
The relationship between brightness, color,
and position of material in the image indicates
where in the star this material was just before
the explosion.
Bright knots on the left, for example, contain little iron,
and so are
hypothesized to originated from a higher layer
than outer red filaments, which are iron rich.
The blue region on the right is seen through absorbing
dust,
and so appears depleted of low-energy X-rays.
It takes light ten years to cross the gas shell of the
Cas A supernova remnant, which is 10,000
light-years distant.
Most of the
elements
that make people and planets were produced in
supernova explosions.
APOD: December 16, 1999 - Supernova Remnant In M82
Explanation:
This false-color radio wavelength picture
of an expanding stellar debris cloud
is the product of one of the
largest radio astronomy experiments ever.
Combining the output of 20 radio telescopes
scattered around planet Earth,
astronomers have produced this amazingly detailed
image of a supernova remnant just over 1.5 light-years across in
M82,
an intense star forming galaxy 12 million light-years away.
The radio astronomy
technique for creating the earth-sized
array of telescopes is known as
VLBI (very long baseline
interferometry).
The individual telescopes of the array are too far apart for
all their signals to be combined in "real time", so their output
was recorded on magnetic tapes which were
brought to a single location and
correlated.
This technique has produced the highest resolution
astronomical observations currently possible and
allows the exploration of such distant,
violent galactic environments
in unprecedented detail.
APOD: December 9, 1999 - X-ray Hot Supernova Remnant in the SMC
Explanation:
The Q-shaped cloud seen in
this false-color X-ray image
from the orbiting Chandra Observatory is big ... about
40 light-years across.
It's hot too, as its
X-ray glow is produced by multi-million
degree gas.
Cataloged as E0102-72, this cosmic Q is likely a
several thousand year old
supernova remnant, the
result of the death explosion of a massive star.
A supernova can dramatically affect its galactic
environment, triggering star formation
and enriching
the local interstellar medium with newly
synthesized elements.
This supernova remnant is
located about 210,000 light-years away in our neighboring galaxy, the
Small Magellanic Cloud (SMC), so the detailed Chandra
X-ray image
is impressive - particularly as it reveals
what appear to be strange spoke-like
structures radiating from the remnant's center.
APOD: November 27, 1999 - Runaway Star
Explanation:
Runaway stars are massive stars
traveling rapidly through interstellar space.
Like a ship plowing through
the interstellar medium,
runaway star HD 77581 has produced this graceful arcing bow wave or "bow
shock" - compressing the gaseous material in its path.
Located near the centre of
this European Southern Observatory photograph,
HD 77581 itself is so bright that it saturates the sensitive camera and
produces the spiky
cross shape.
This star is over 6,000 light-years away in
the constellation Vela, and
appears to move at over 50 miles per second.
What force could set this star in motion?
A clue to the answer may lie in its optically invisible companion star, an
X-ray bright
pulsar known as Vela X-1.
This pulsar is clearly the remnant of
a supernova explosion ...
which seems to have given this massive star and
its companion a mighty kick!
APOD: November 22, 1999 - The Crab Nebula from VLT
Explanation:
The Crab Nebula, filled with mysterious filaments, is the result of a
star that was seen to explode in 1054 AD.
This spectacular supernova explosion was recorded by Chinese and (quite probably) Anasazi Indian astronomers.
The filaments are mysterious because they appear
to have less mass than expelled in the original supernova
and higher speed than expected from a free explosion.
In the above picture taken recently from a
Very Large Telescope,
the color indicates what is happening to the electrons in different
parts of the Crab Nebula.
Red indicates the electrons are recombining with protons to form neutral hydrogen,
while blue indicates the electrons are whirling around the magnetic field
of the inner nebula.
In the
nebula's very center lies a pulsar: a neutron star rotating, in this case, 30 times a second.
APOD: September 13, 1999 - Supernova Remnant N132D in X Rays
Explanation:
Thousands of years after a star explodes,
an expanding remnant may still glow brightly.
Such is the case with
N132D, a
supernova remnant
located in the neighboring
Large Magellanic Cloud galaxy.
The expanding shell
from this explosion now spans 80
light-years and has swept up about 600 Suns worth of mass.
The bright regions surrounding the lower right of this
X-ray image result from a collision with an even more massive
molecular cloud.
Towards the upper left, the
supernova remnant expands more rapidly into
less dense region of space.
This image is one of the first ever taken with the
High Resolution Camera onboard the orbiting
Chandra X-ray Observatory,
and records details being analyzed for the first time.
APOD: August 27, 1999 - Chandras First Light: Cassiopeia A
Explanation:
Cosmic wreckage from the detonation of a massive star is the
subject of
this official first image from NASA's
Chandra X-ray Observatory.
The supernova remnant, known as
Cassiopeia A, was produced when
a star exploded around 300 years ago in
this northern sky constellation.
It is revealed here in unprecedented
detail in the
light of X-rays - photons with thousands of times the energy
of visible light.
Shock waves expanding at 10 million miles-per-hour
are seen to have heated this 10 light-year diameter
bubble of stellar debris
to X-ray emitting temperatures of 50 million
kelvins.
The tantalizing bright speck near the bubble's center could
well be the dense, hot remnant of the stellar core collapsed to form a
newborn neutron star.
With this and other
first light images, the Chandra
Observatory is still undergoing check out operations in preparation
for its much anticipated exploration of the X-ray sky.
Chandra was launched
aboard the space shuttle Columbia in July.
APOD: August 3, 1999 - The Vela Supernova Remnant Expands
Explanation:
The explosion is over but the consequences continue.
About eleven thousand years ago a star in the constellation of Vela exploded, creating a
strange point of light briefly visible to humans living near the
beginning of recorded history.
The outer layers of the star crashed into the
interstellar medium, driving a
shock wave that is still
visible today.
Different colors in the complex, right moving shock,
pictured on the left, represent
different energies of impact of the
shock front. The star on the left appears by chance in the foreground, and the long diagonal line is also unrelated.
Remaining at the center of the
Vela Supernova Remnant is a
pulsar, a star as dense as
nuclear matter that completely rotates more than
ten times in a single second.
APOD: July 25, 1999 - The Cygnus Loop
Explanation:
The shockwave from a 20,000 year-old supernova
in the constellation of Cygnus
supernova explosion is
still expanding into interstellar space.
The collision of this fast moving wall of gas with
a stationary cloud has heated it causing it to
glow in visible as well as
high energy radiation, producing the nebula known as the
Cygnus Loop (NGC 6960/95).
The nebula is located about 2500 light-years away.
The colors used here indicate emission from
different kinds of atoms excited by the
shock:
oxygen-blue, sulfur-red, and hydrogen-green.
This picture was taken with
the Wide Field and Planetary Camera 2 on board the
Hubble Space Telescope.
APOD: July 21, 1999 - Galactic Supernova Remnant IC 443
Explanation:
About 8000 years ago, a star in our Galaxy exploded.
Ancient humans might have noticed the
supernova as a temporary star,
but modern humans can see the expanding shell
of gas even today.
In the
above false-color infrared image of
supernova remnant IC 443,
blue denotes expanding gas where
emission is dominated by excited iron atoms.
Of particular interest, though, are the wisps of
IC 443 colored red,
as they are impacting an otherwise normal
molecular cloud.
Here emission from shock-excited molecular
hydrogen is allowing
astronomers to study how fast moving supernova
gas affects star formation in the cloud.
Additionally,
astronomers theorize that the impact accelerates
some particles to velocities near the speed of light.
The horizontal line across the image is not part of the nebula.
APOD: June 4, 1999 - NGC 3603: From Beginning To End
Explanation:
From beginning to end, different stages of a star's life appear in
this exciting Hubble Space Telescope picture of the environs
of galactic emission nebula
NGC 3603.
For the beginning, eye-catching "pillars" of glowing
hydrogen at the right signal
newborn stars emerging
from their dense, gaseous, nurseries.
Less noticeable,
dark clouds
or "Bok globules" at the top
right corner are likely part of a still earlier stage, prior to their
collapse to form stars.
At picture center lies a cluster of bright
hot blue stars whose strong
winds and ultraviolet radiation have cleared away nearby material.
Massive and young, they will soon exhaust their nuclear fuel.
Nearing the end of its life, the bright supergiant
star Sher 25 is
seen above and left of the cluster, surrounded by a glowing ring and flanked
by ejected blobs of gas.
The ring structure is reminiscent of
Supernova 1987a and Sher 25
itself may be only a few thousand years from its
own devastating finale.
But what about planets?
Check out the two
teardrop-shaped objects below the cluster
toward the bottom of the picture.
Although larger, these emission nebulae are similar to suspected
proto-planetary disks (proplyds) encompassing stars in the Orion Nebula.
APOD: May 15, 1999 - Star Wars in NGC 664
Explanation:
Long ago in a galaxy far, far away,
locked in their final desperate struggle against the force of gravity ...
two stars exploded!
stellar explosions -
Supernovae - are
among the most powerful
events in the Universe, estimated to
release an equivalent energy of up to
1 million trillion trillion (1 followed by 30 zeros) megatons of TNT.
After the explosion, an expanding supernova envelope
is observed to brighten over a
a period of days to a maximum light output
which rivals that of an entire galaxy before
fading from view over the following months.
Triggered by the collapsing core of a massive star or the
nuclear demise of a white dwarf
supernovae occur in average spiral galaxies
only about once every 25-100 years.
But a recent observation of NGC 664, a spiral galaxy about 300 million
light years distant, captured a rare and colorful performance -
two supernovae from the same galaxy.
In this monitoring exposure the two supernovae,
one reddish yellow and one blue, form a close pair
just below the image center (to the right of the galaxy nucleus).
The color difference is due to temperature -
blue is hotter.
APOD: May 3, 1999 - Loop I in the Northern Sky
Explanation:
One of the largest coherent structures
on the sky is known simply as
Loop I and can best be seen in
radio and
X-ray maps.
Spanning over 100 degrees, part of
Loop I appears so prominent in
northern sky maps that it is known as the
North Polar Spur (NPS).
Loop I, shown above in
X-ray light,
is a thin bubble of gas about 700 light-years across
with a center located only about 400 light-years away.
Surprisingly, the cause of this immense structure
is still debated, but is possibly related to expanding
gas from a million-year old
supernova.
Loop I gas is impacting the nearby
Aquila Rift
molecular cloud,
and may create relatively dense fragments of the local
interstellar medium.
Were our Sun to pass through one of these fragments
in the next few million years, it
might affect Earth's climate.
APOD: April 13, 1999 - The Case of the Missing Supernova
Explanation:
Would you notice a second Moon in the sky?
About 700 years ago, light from a
tremendous explosion reached Earth
that should have appeared almost
as bright as a full Moon.
The bright spot should have lasted for weeks,
yet no notation of such an occurrence
has been found in historical records.
The mystery was uncovered by
Wan Chen and Neil Gehrels
(NASA/GSFC) when studying the source of
radioactive elements toward the
Vela supernova remnant.
They deduced that an explosion
much younger and closer than the
supernova that caused
Vela must have occurred, and even computed
explosion characteristics from the amounts of
radioactive elements present.
They calculate that GRO/RX J0852 should
have dazzled
medieval stargazers.
Perhaps people were too busy,
surviving records are too incomplete,
or the explosion was somehow too dim.
The
above picture of GRO/RX J0852 was taken in
gamma-ray light with the
Compton Gamma-Ray Observatory
and is shown in false-color.
Astronomers and historians continue to contemplate the clues.
APOD: April 7, 1999 - Denizen of the Tarantula Nebula
Explanation:
The star cluster at lower right,
cataloged as Hodge 301, is a
denizen of
the Tarantula Nebula.
An evocative nebula in the southern sky,
the sprawling cosmic Tarantula is
an energetic star forming region some 168,000 light-years distant
in our neighboring galaxy the
Large Magellanic Cloud.
The stars within Hodge 301 formed together tens of millions of years ago
and as the massive ones quickly exhaust their nuclear fuel they
explode.
In fact, the red giant stars of Hodge 301 are rapidly approaching
this violent final phase of stellar evolution -
known as a supernova.
These supernova blasts send material and
shock waves back into the nebular
gas to create the Tarantula's glowing filaments also visible in
this Hubble Space Telescope Heritage image.
But these spectacular stellar death explosions signal star birth
as well, as the blast waves condense gas and dust to ultimately
form the next generation of stars
inside the Tarantula Nebula.
APOD: March 7, 1999 - Tychos Supernova Remnant in X ray
Explanation:
How often do stars explode? By looking at external galaxies,
astronomers can guess that these events,
known as a supernovae, should occur about once every
30 years in a typical spiral galaxy
like our MilkyWay.
However, the obscuring gas and dust in the disk of our galaxy
probably prevents us from seeing many galactic supernovae -- making
observations of these events in our own galaxy relatively rare.
In fact, in 1572, the revered
Danish astronomer, Tycho Brahe,
witnessed one of the last to be seen.
The remnant of this explosion is still visible today as the
shockwave it generated continues to expand into
the gas and dust between the stars.Above is an image of the X-rays emitted by this
shockwave made by a telescope onboard the
ROSAT spacecraft.
The nebula is known as Tycho's Supernova Remnant.
APOD: February 9, 1999 - A Supernova Starfield
Explanation:
Bright stars don't last forever. A
bright star
similar to others in this field exploded in a spectacular supernova that was
witnessed on Earth in 1987.
The result is visible even today as
unusual rings
and glowing gas. The
above picture is a composite of recent images taken over several years.
The explosion originated from a bright massive star that
ran out of nuclear fuel.
SN1987A occurred in the
Large Magellanic Cloud
(LMC), a satellite galaxy only 150,000 light years from our
Milky Way Galaxy.
The rings of
SN1987A
are currently excited by light from the initial explosion.
Astronomers expect the
inner ring to brighten
in the next few years as expanding supernova debris
overtakes it.
APOD: December 30, 1998 - Supernova 1994D and the Unexpected Universe
Explanation:
Far away, long ago, a star exploded.
Supernova 1994D, visible as the bright spot on the lower left,
occurred in the outskirts of disk galaxy NGC 4526.
Supernova 1994D was not of interest for how different it was,
but rather for how similar it was to other supernovae.
In fact, the light emitted during the
weeks after its explosion caused it to be given
the familiar designation of a Type Ia supernova.
If all Type 1a supernovae have the same intrinsic brightness,
then the dimmer a supernova appears, the farther away it must be.
By calibrating a precise
brightness-distance relation,
astronomers are able to estimate not only the
expansion rate of the universe (parameterized by the
Hubble Constant),
but also the
geometry of the universe we live in
(parameterized by
Omega and
Lambda).
The large number and great distances to supernovae measured in 1998
have been interpreted
as indicating that we live in a
previously unexpected universe.
APOD: November 22, 1998 - The High Energy Crab Nebula
Explanation:
This is the mess that is left when a star explodes. The
Crab Nebula
is so energetic that it glows in
every kind of light known.
Shown above are images of the
Crab Nebula from visible light to the
X-ray band.
NUV stands for "near
ultraviolet" light, FUV means "far
ultraviolet" light, and VIS means visible light. In the center of the
Crab Nebula lies the powerful
Crab pulsar - a spinning
neutron star with mass comparable to our
Sun but with the diameter of only a
small town.
The pulsar expels particles and radiation in a beam that sweeps past the
Earth 30 times a second. The
supernova that created the
Crab Nebula was seen by
ancient
Chinese astronomers and possibly even the
Anasazi Indians -- in 1054 AD, perhaps glowing for a
week as bright as the
full moon. The
Crab
still presents mysteries today as the total mass of the nebula and pulsar appears much less than the mass of the original pre-supernova star!
APOD: August 16, 1998 - Doomed Star Eta Carinae
Explanation:
Eta Carinae may be about to explode. But no one knows when - it may be
next year, it may be one million years from now.
Eta Carinae's mass - about
100 times greater than our Sun -
makes it an excellent candidate for a full blown supernova.
Historical records do show that about 150 years
ago Eta Carinae underwent an unusual outburst that made it one of the brightest stars in the southern sky.
Eta Carinae, in the
Keyhole Nebula, is
the only star currently
thought to emit natural LASER light. This
image, taken in 1996, resulted from sophisticated
image-processing procedures designed to bring out new details in the
unusual nebula that surrounds
this
rogue star. Now clearly visible are two
distinct lobes, a hot central
region, and strange radial streaks.
The lobes are filled with lanes of gas and dust which absorb the blue and
ultraviolet light emitted near the center. The streaks remain unexplained.
Will these clues tell us how the nebula was formed?
Will they better indicate when
Eta
Carinae will explode?
APOD: August 8, 1998 - The Cygnus Loop
Explanation:
15,000 years ago a star in the constellation of Cygnus exploded --
the shockwave from this
supernova explosion is
still expanding into interstellar space!
The collision of this fast moving wall of gas with
a stationary cloud has heated it causing it to
glow in visible as well as
high energy radiation, producing the nebula known as
the Cygnus Loop (NGC 6960/95).
The nebula is located about 2500 light years away.
The colors used here indicate emission from different kinds of atoms
excited by the shock; oxygen-blue, sulfur-red, and hydrogen-green.
This picture was taken with
the Wide Field and Planetary Camera 2 on board the
Hubble Space Telescope.
APOD: July 31, 1998 - IRAS Orion
Explanation:
Do you recognize the
constellation Orion?
This striking but unfamiliar looking picture of
the familiar
Orion region of the sky was produced
using survey data from the
InfraRed Astronomical Satellite (IRAS).
It combines information recorded
at three different
invisible infrared wavelengths
in a red, green, and blue color scheme
and covers about 30x24 degrees on the sky.
Most of Orion's visually impressive stars don't stand out,
but bright Betelgeuse
does appear as a small purplish dot just above center.
Immediately to the right of Betelgeuse and prominent in the IRAS
skyview,
expanding debris from a stellar explosion,
a supernova remnant,
is seen as a large bright ring-shaped feature.
The famous
gas clouds
in Orion's sword glow brightly as the yellow
regions at the lower right.
No longer operational,
IRAS used a telescope cooled by liquid
helium to detect
celestial infrared radiation.
APOD: June 18, 1998 - Cosmic Rays and Supernova Dust
Explanation:
Cosmic Rays
are celestial high energy particles traveling
at nearly the speed of light, which constantly bombard the Earth.
Discovered during
high altitude balloon flights in 1912
their source has been a long standing mystery.
But a recent theory suggests that
cosmic ray particles are
atomic nuclei blasted from dust grains
formed in supernovae, the death explosions of massive stars.
This artist's illustration shows a supernova explosion
(at left) and a conical
section of the expanding cloud
of ejected material.
Atoms are torn from the brownish bands of
"dust"
material by shock waves (represented by orange rings).
The shocks in the expanding blast wave
then accelerate the atoms
to near light speeds firing them into interstellar space like
cosmic bullets.
The theory is supported by observations indicating
that high velocity dust was formed in
the nearby supernova 1987A,
and that Beryllium, a light element created in
Cosmic Ray collisions, is found equally in both old an young stars.
NASA's
Advanced Composition Explorer (ACE) satellite can also test details of
the theory by directly measuring Cosmic Rays.
APOD: May 8, 1998 - A Gamma Ray Burst Supernova
Explanation:
Did a gamma-ray burst precede this
supernova? This
intriguing suggestion came to light yesterday with the discovery of an evolving supernova
that is potentially coincident with the position of
gamma-ray burst
GRB 980425, which occurred just
two weeks ago.
If true, this would tie together the two most
violent phenomena
known in the universe. The supernova,
indicated by the arrow, appears to be somewhat unusual,
for one reason because of its extremely bright radio emission. The
host galaxy
has a redshift of 0.0085, placing it at the relatively
close distance of about 125 million light years away.
Today it remains undetermined whether the
two events are related - perhaps the evolution of the
supernova over the
next few weeks will provide some clues.
APOD: April 25, 1998 - Supernova Remnant and Neutron Star
Explanation:
A massive star ends life as a supernova, blasting
its outer layers back to interstellar space.
The spectacular death explosion is
initiated by the collapse of what has become an impossibly dense
stellar core.
However, this core is not necessarily destroyed. Instead, it may be
transformed into an exotic object with the density of an
atomic nucleus but more total mass
than the sun -
a neutron star.
A neutron star is hard to detect directly because it is
small (roughly 10 miles in diameter)
and therefore dim, but newly formed in this violent crucible
it is intensely hot,
glowing in X-rays.
These
X-ray images from the orbiting ROSAT observatory may offer a premier
view of such a recently formed neutron stars' X-ray glow.
Pictured is the supernova
remnant Puppis A, one of the brightest
sources in the X-ray sky,
with shocked gas clouds still expanding and
radiating X-rays. In the inset close-up view,
a faint pinpoint source of X-rays is visible which is most likely
the young neutron star,
kicked out by the asymmetric explosion and
moving away from the site of the original supernova at about 600 miles
per second.
APOD: April 18, 1998 - Star Wars in NGC 664
Explanation:
Long ago in a galaxy far, far away,
locked in their final desperate struggle against the force of gravity ...
two stars exploded!
stellar explosions -
Supernovae - are
among the most powerful
events in the Universe, estimated to
release an equivalent energy of up to
1 million trillion trillion (1 followed by 30 zeros) megatons of TNT.
After the explosion, an expanding supernova envelope
is observed to brighten over a
a period of days to a maximum light output
which rivals that of an entire galaxy before
fading from view over the following months.
Triggered by the collapsing core of a massive star or the
nuclear demise of a white dwarf
supernovae occur in average spiral galaxies
only about once every 25-100 years.
But a recent observation of NGC 664, a spiral galaxy about 300 million
light years distant, captured a rare and colorful performance -
two supernovae from the same galaxy.
In this monitoring exposure the two supernovae,
one reddish yellow and one blue, form a close pair
just below the image center (to the right of the galaxy nucleus).
The color difference is due to temperature -
blue is hotter.
APOD: March 2, 1998 - Rumors of a Strange Universe
Explanation:
In a
meeting in California two weeks ago, unpublished results were presented indicating that
most of the energy in our universe is not in stars or galaxies but
is tied to space itself.
In the language of cosmologists, a large
cosmological constant is directly implied by new distant
supernovae observations.
Suggestions of a cosmological constant (lambda) are
not new -- they have existed since the advent of
modern relativistic cosmology. Such claims are
not usually popular with astronomers, though,
because lambda is so unlike known universe components,
because
lambda's value appears limited by observations,
and because less-strange cosmologies without lambda
have historically done well in explaining the data.
Therefore most lamdba claims do not make the News Summary in a
prestigious journal like
Science.
What is noteworthy here is the seemingly direct
and reliable method of the observations,
and the good reputations of the scientists conducting the investigation. The
above picture of a supernova at redshift 0.5 in a
spiral galaxy, was taken
by this collaboration.
However, two teams of scientists are
independently studying
distant supernovae,
and the last official word from the other team was a result consistent with no cosmological constant,
reported just two months ago.
Extraordinary claims require extraordinary evidence,
and so cosmologists the world over eagerly await
peer-reviewed results, further details, and more data.
APOD: February 17, 1998 - Shocked by Supernova 1987a
Explanation:
Eleven years ago the brightest
supernova of modern times
was recorded. Now the expanding debris from this
tremendous stellar explosion is seen to be
crashing into
previously expelled material.
The onset of this collision is shown by the arrow in the
above picture as the yellow spot on the interior of the ring.
Although the collision is occurring at speeds near
60 million km/hour, it will appear to take years due
to the vast distances involved. As the
supernova blast wave moves out, it
shock-heats any gas it encounters, causing it to glow.
Astronomers are thus hopeful that the blast wave will
illuminate the interesting past of SN 1987a, and perhaps provide more clues
about the origins of the
mysterious rings.
APOD: February 11, 1998 - Ultra Fast Pulsar
Explanation:
Pulsars are rotating
neutron stars, born in the violent
crucibles of supernova explosions.
Like cosmic lighthouses, beams of radiation from surface hotspots sweep
past our viewpoint creating pulses which reveal the rotation rates
of these incredibly dense stellar corpses.
The most famous pulsar of all is found in the nearby supernova
remnant, the Crab Nebula.
The Crab's young pulsar is fast.
Rotating at 33 times a second,
its radiation energizes the surrounding
gaseous stellar debris.
But using
archival observations from orbiting X-ray telescopes,
astronomers have recently identified another "Crab-like" pulsar
that is even faster.
Located in the Large Magellanic Cloud (LMC),
X-ray pulses from this newly discovered pulsar,
in the supernova remnant N157B,
indicate an even faster rotation rate - 62 times a second -
making it
the fastest known pulsar associated with a supernova remnant.
This contoured, false color X-ray image of
a portion of the LMC
shows the location of N157B along with
the core of the nearby
hot star cluster R136,
and the site of another Crab-like pulsar in SNR 0540-69.3
(rotating a mere 20 times a second).
The image is about 1,500 light-years across.
APOD: February 8, 1998 - M1: Filaments of the Crab Nebula
Explanation:
The Crab Nebula, filled with mysterious filaments, is the result of a
star that exploded in 1054 AD.
This spectacular supernova
explosion was recorded by Chinese and (quite probably) Anasazi Indian astronomers.
The filaments are mysterious because they appear
to have less mass than expelled in the original supernova
and higher speed than expected from a free explosion.
In the above picture, the color indicates what is
happening to the electrons in different
parts of the Crab Nebula.
Red indicates the electrons are recombining with protons to form neutral hydrogen,
while green indicates the electrons are whirling around the magnetic field
of the inner nebula. In the nebula's
very center lies a pulsar: a neutron star rotating, in this case, 30 times a second.
APOD: December 14, 1997 - The Radio Sky: Tuned to 408MHz
Explanation:
Tune your radio telescope to 408MHz
(408 million cycles per second) and check out the Radio Sky!
You should find that frequency on your
dial somewhere between
US broadcast television channels 13 and 14.
In the 1970s large dish antennas at
three radio observatories, Jodrell Bank,
MPIfR, and
Parkes Observatory,
were used to do just that -
the data were combined to map the entire sky.
Near this frequency,
cosmic radio waves are generated by high energy electrons spiraling
along magnetic fields.
In the resulting false color image, the galactic plane
runs horizontally through the center, but no
stars are visible.
Instead, many of the bright sources near the plane
are distant pulsars, star forming regions,
and supernova remnants,
while the grand looping structures
are pieces of
bubbles blown by local stellar activity.
External galaxies like
Centaurus A, located above the plane to the
right of center, and
the LMC (below and right)
also shine in the radio sky.
APOD: December 3, 1997 - Runaway Star
Explanation:
Runaway stars are massive stars
traveling rapidly through interstellar space.
Like a ship plowing through
the interstellar medium,
runaway star HD 77581 has produced this graceful arcing bow wave or "bow
shock" - compressing the gaseous material in its path.
Located near the centre of
this European Southern Observatory photograph,
HD 77581 itself is so bright that it saturates the sensitive camera and
produces the spiky cross shape.
This star is over 6,000 light-years away in
the constellation Vela, and
appears to move at over 50 miles per second.
What force could set this star in motion?
A clue to the answer may lie in its optically invisible companion star, an
X-ray bright
pulsar known as Vela X-1.
This pulsar is clearly the remnant of
a supernova explosion ...
which seems to have given this massive star and
its companion a mighty kick!
APOD: October 24, 1997 - Moving Echoes Around SN 1987A
Explanation:
Yesterday's image
highlighted reflective rings of light emitted by a
supernova explosion.
Today's pictures, taken over a year apart,
highlight how these echoes are seen to move over time.
Visible on the left of each picture is part of a reflective ring,
an existing
dust cloud momentarily
illuminated by the light of Supernova 1987A. Note how the nebulosity reflecting
the most light occurs farther to the left in the lower photograph.
If you look closely, you can see the actual location of
SN 1987A itself on the right
of each photograph: it appears in the center of a small yellowish ring.
The apparent motion and brightness of these echoes help astronomers
understand the abundance and distribution of
interstellar nebulae
in the LMC galaxy,
where the
stellar explosion occurred.
APOD: October 23, 1997 - Echoes of Supernova 1987A
Explanation:
Can you find
Supernova 1987a?
It's not hard - it occurred in the center of the bulls-eye pattern. Although this
stellar
detonation was seen more than a decade ago,
light from it continues to bounce off nearby
interstellar dust and be reflected to us.
These two rings are thus echoes of the powerful
supernova.
As time goes on, these echoes appear to expand outward from the center.
The above image was created by subtracting a picture taken
before 1987, from a picture taken after.
APOD: October 2, 1997 - Colliding Supernova Remnants
Explanation:
When a massive
star exhausts its nuclear fuel
it explodes.
This stellar detonation,
a supernova,
propels vast amounts of
starstuff outwards,
initially at millions of miles per hour.
For another 100,000 years or so the expanding
supernova remnant
gradually slows as it
sweeps up material and
ultimately merges
with the gas and dust of
interstellar space.
Short lived by cosmic standards, these stellar debris clouds
are relatively rare and valuable objects for astronomers
exploring
the life cycles of stars.
Yet this
double bubble-shaped nebula 160,000 light-years away in
the Large Magellanic Cloud
may represent something rarer still - the collision of two
supernova remnants.
This image in the light of excited Hydrogen atoms along
with images at X-Ray, radio and other optical
wavelengths, suggests that
the bubbles are indeed two separate regions of hot gas surrounded by cooler
dense shells begining to interact as they expand and make contact.
APOD: August 12, 1997 - Sher 25: A Pending Supernova?
Explanation:
No supernova
has ever been predicted - yet. These
dramatic stellar explosions
that destroy stars, that create and disperse the elements
that compose
people and
planets, that
light up the night sky,
are not so well understood that astronomers can accurately
predict when a star will explode - yet. Perhaps Sher 25 will be the first. Sher 25, designated by the arrow, is a blue
supergiant
star located just outside the
open star cluster and
ionized
region named NGC 3603. Sher 25 lies in the center of an
hourglass shaped nebula much like the
one that surrounds the last bright supernova visible from Earth:
SN1987a. Now the hourglass shaped rings around
SN1987a
were emitted before that blue supergiant
exploded.
Maybe Sher 25 has expelled these bipolar rings in a step that closely precedes a
supernova.
Maybe not. If so, Sher 25 may be within a few thousand years of its spectacular finale.
APOD: July 13, 1997 - Vela Supernova Remnant in Optical
Explanation:
About 11,000 years ago a star in the constellation of
Vela exploded.
This bright
supernova
may have been visible to the
first human farmers. Today the
Vela supernova
remnant marks the position of a relatively close and
recent explosion in
our Galaxy.
A roughly
spherical, expanding shock wave
is visible in X-rays. In the
above optical photograph, the upper left
corner of the spherical blast wave is shown in detail. As
gas flies away from the detonated star, it reacts with the
interstellar medium, knocking away closely held
electrons from even
heavy elements. When the
electrons recombine with these atoms, light in
many different colors and
energy bands is produced.
APOD: May 2, 1997 - X-Rays From IC 443
Explanation:
The life-cycles of stars help drive the ecology of our Galaxy,
churning, processing, and redistributing matter.
Massive stars reach a spectacular evolutionary endpoint -
supernovae explosions which blast off
their outer layers, violently merging stellar material with the
gas and dust of the Milky Way.
The supernova remnant IC 443 is typical of the aftermath. Seen in
this false color
X-ray image are the shocked,
expanding shells of gas from a star which
exploded thousands of years ago.
Known to be interacting with
galactic molecular clouds, the expanding
supernova remnant was also recently discovered to have regions of
intense higher energy X-ray emission (coded blue in this map)
near the molecular cloud boundaries.
This X-ray emission may indicate that electrons are
being accelerated within the remnant, gaining in energy as they surf back
and forth across the expanding shock wave.
If so, IC 443 could also be one source of
our Galaxy's puzzling high energy cosmic-rays.
APOD: February 7, 1997 - M1: Filaments of the Crab Nebula
Explanation: The Crab Nebula is filled with mysterious
filaments. The Crab Nebula
is the result of a star that exploded in 1054 AD.
This spectacular supernova
explosion was recorded by Chinese
and (quite probably) Anasazi Indian
astronomers. The filaments are mysterious because they appear
to have less mass than expelled in the original supernova
and higher speed than expected from a free explosion.
In the above picture,
the color indicates what is happening to the electrons in different
parts of the Crab Nebula.
Red indicates the electrons are recombining with protons to form neutral hydrogen,
while green indicates the electrons are whirling around the magnetic field
of the inner nebula. In the nebula's
very center lies a pulsar:
a neutron star
rotating, in this case, 30 times a second.
APOD: January 24, 1997 - Supernova 1987a Fireball Resolved
Explanation: Ten years ago the most notable supernova
of modern times was observed. In February 1987, light reached
Earth from a star which exploded in the nearby Large Magellanic Cloud
galaxy. Supernova 1987a
remains the closest supernova
since the
invention of the telescope.
The explosion
catapulted a tremendous amount of gas,
light,
and neutrinos
into interstellar space. When observed by the Hubble Space Telescope
(HST) in 1994, large strange rings
were discovered whose origin is still mysterious, although thought
to have been expelled even before the main explosion. More recent HST observations
shown in the inset, however, have uncovered something actually predicted:
the expanding fireball from the exploding star. The above high resolution images
resolve two blobs flung out from the central explosion.
APOD: November 14, 1996 - Supernova Remnant and Neutron Star
Explanation:
A massive star ends life as a supernova, blasting
its outer layers back to interstellar space.
The spectacular death explosion is
initiated by the collapse of what has become an impossibly dense
stellar core.
However, this core is not necessarily destroyed. Instead, it may be
transformed into an exotic object with the density of an
atomic nucleus but more total mass
than the sun -
a neutron star.
Directly viewing a neutron star is difficult because it is
small (roughly 10 miles in diameter)
and therefore dim, but newly formed in this violent crucible
it is intensely hot,
glowing in X-rays.
Images from the ROSAT X-ray observatory above may offer a premier
view of such a recently formed neutron stars' X-ray glow.
Pictured is the supernova
remnant Puppis A, one of the brightest
sources in the X-ray sky,
with shocked gas clouds still expanding and
radiating X-rays. In the inset close-up view,
a faint pinpoint source of X-rays is visible which is most likely
the young neutron star,
kicked out by the asymmetric explosion and
moving away from the site of the original supernova at about 600 miles
per second.
APOD: October 16, 1996 - SN 1006: Pieces of the Cosmic Ray Puzzle
Explanation:
Research balloon flights conducted in 1912 by Austrian physicist Victor Hess
revealed that the Earth was constantly bombarded by high energy
radiation from space - which
came to be called "Cosmic Rays".
What are Cosmic Rays and where do they come from?
They are now known to be mostly subatomic particles - predominantly
protons and electrons -
but their origin is a long standing mystery.
After almost a century of study,
this cosmic puzzle may have been at least partially solved by new
X-ray images and spectra from the
ASCA satellite observatory.
Pieced together to show the region around a star observed to go
supernova in 1006 AD, the overlapping X-ray snapshots above
(seen in false color) reveal the bright rims of
the exploded star's still expanding blast wave.
These ASCA observations show for the
first time that the energy spectrum of the bright regions is like that
produced by extremely high energy electrons
streaming through a magnetic field at nearly the speed of light.
If (as expected) high energy protons are associated with
these energetic electrons
then supernova remnants like SN 1006 are sources of Hess'
puzzling Cosmic Rays.
APOD: September 9, 1996 - The High Energy Crab Nebula
Explanation:
This is the mess that is left when a star explodes. The
Crab Nebula
is so energetic that it glows in
every kind of light known.
Shown above are images of the
Crab Nebula from visible light to the
X-ray band.
NUV stands for "near
ultraviolet" light, FUV means "far
ultraviolet" light, and VIS means visible light. In the center of the
Crab Nebula lies the powerful
Crab pulsar - a spinning
neutron star
with mass comparable to our
Sun but with the diameter of only a
small town.
The pulsar expels particles and radiation in a beam that sweeps past the
Earth 30 times a second. The
supernova that created the
Crab Nebula was seen by
ancient
Chinese astronomers and possibly even the
Anasazi Indians
-- in 1054 AD, perhaps glowing for a week as bright as the
full moon. The Crab
still presents mysteries today as the total mass of the nebula and pulsar appears much less than the mass of the original pre-supernova star!
APOD: July 5, 1996 - The Mysterious Rings of Supernova 1987a
Explanation:
What's causing those odd rings in
supernova 1987a?
In 1987, the brightest
supernova
in recent history occurred in the
Large Magellanic Clouds. At the
center of the picture is an object central to the remains of the violent
stellar explosion. When the
Hubble Space Telescope was pointed at the
supernova remnant
in 1994, however,
curious
rings were discovered. The
origins of these rings still remains a mystery. Speculation into the cause
of the rings includes
beamed jets emanating from a dense star left over
from the supernova, and a
superposition of two stellar winds ionized by the
supernova explosion.
APOD: June 23, 1996 - Tycho's Supernova Remnant in X-ray
Explanation:
How often do stars explode? By looking at external galaxies,
astronomers can guess that these events,
known as a supernovae, should occur about once every
30 years in a typical spiral galaxy
like our MilkyWay.
However, the obscuring gas and dust in the disk of our galaxy
probably prevents us from seeing many galactic supernovae -- making
observations of these events in our own galaxy relatively rare.
In fact, in 1572, the revered
Danish astronomer, Tycho Brahe,
witnessed one of the last to be seen.
The remnant of this explosion is still visible today as the
shockwave it generated continues to expand into
the gas and dust between the stars.
Above is an image of the X-rays emitted by this
shockwave made by a telescope onboard the
ROSAT spacecraft.
The nebula is known as Tycho's Supernova Remnant.
APOD: June 13, 1996 - Vela Supernova Remnant in Optical
Explanation:
About 11,000 years ago a star in the constellation of
Vela exploded.
This bright
supernova
may have been visible to the
first
human farmers. Today the
Vela supernova
remnant marks the position of a relatively close and
recent explosion in
our Galaxy.
A roughly
spherical, expanding shock wave
is visible in X-rays. In the
above optical photograph, the upper left
corner of the spherical blast wave is shown in detail. As
gas flies away from the detonated star, it reacts with the
interstellar medium, knocking away closely held
electrons from even
heavy elements. When the
electrons recombine with these atoms, light in
many different colors and
energy bands is produced.
APOD: June 12, 1996 - Vela Supernova Remnant in X-ray
Explanation:
What happens when a
star explodes? A huge fireball of hot
gas shoots out
in all directions. When this gas slams into the existing
interstellar medium,
it heats up so much it glows in
X-rays. The
above
picture by the
ROSAT satellite has captured some of these X-rays and shown -- for the
first time -- the
Vela supernova
explosion was roughly spherical.
Non-uniformity of the interstellar medium causes Vela's appearance to be
irregular. The size of this X-ray emitting spherical shell is immense -
230 light years across, covering over 100 times the sky-area of the full
Moon. The
supernova
that created this nebula occurred about 1500 light
years away and about 11,000 years ago. Coincidently, a completely different
supernova shell can also be seen in X-rays in this picture! It is visible
as the bright patch near the upper right. This
Puppis supernova remnant nebula is actually about four times farther
than the Vela nebula.
APOD: May 9, 1996 - Supernova Remnant: Cooking Elements In The LMC
Explanation:
Massive stars cook elements in their cores through
nuclear fusion. Starting
with the light elements of hydrogen and helium, their central
temperatures and pressures produce progressively heavier elements,
carbon, oxygen, nitrogen, etc. up through iron.
At the end of their lives they explode in
a spectacular supernova,
scattering these elements into space, contributing
material to the formation of other stars and star systems.
In fact, the elements making up
life on Earth were baked in such
a stellar oven!
This Hubble Space Telescope image
of a supernova remnant known as N132D
in the Large Magellanic Cloud (LMC)
allows astronomers to
explore the details
of this nuclear processing and mixing.
It reveals luminous clouds of cooked supernova debris
energized by shocks -- singly
ionized sulfur appears red, doubly ionized oxygen, green, and singly ionized
oxygen, blue. The region shown above is about 50 lightyears across.
APOD: April 21, 1996 - A Supernova in the Whirlpool
Explanation:
In 1994, a new star in a distant galaxy
was seen by amateur
astronomers, who alerted the world to their discovery of a
supernova.
Near the nucleus of spiral galaxy M51,
popularly known as the Whirlpool,
this supernova (1994I) is identified as the bright spot indicated
by the arrow in the lower left of
this Hubble Space Telescope image.
Supernovae are violent death explosions of stars
that eject radioactive debri clouds.
They are often discovered by
amateur observers dedicated to systematic
searches of the sky and are of
intense interest to astronomers
who hope to learn what kind of stars generate these explosions
and what chemical elements are produced and mixed into space.
Distances to these
these intrinsically bright events can also be determined, providing
crucial yardsticks for measuring
the Scale of the Universe.
APOD: March 7, 1996 - Rampaging Fronts of the Veil Nebula
Explanation:
A supernova explosion of a high-mass star results in fast moving blast
waves. At the front of the waves shown above, ionized gas in the
Veil
Supernova Remnant rushes out from the explosion, sweeps up material, and
breaks up many atoms into constituent ions and electrons.
Observations with
the Hubble Space Telescope
in 1993 indicate that the blue shock wave was
catapult away from the stellar explosion after the red shock wave and has
yet to catch up to it in some regions. The Veil supernova remnant's has a
very large angular size - six times the diameter of the full moon - and
different parts of it are known as the
"Cygnus Loop" and catalog numbers
NGC 6960, NGC 6979, NGC 6992, and NGC 6995.
APOD: February 20, 1996 - ASCA X-Ray Observatory
Explanation:
Today marks the third anniversary of the launch of the Advanced Satellite
for Cosmology and Astrophysics (ASCA; renamed from Astro D when launched).
ASCA, seen here superposed on galaxy
M31, is a Japanese satellite for
which NASA has provided some scientific equipment.
ASCA
carries four large-area X-ray telescopes. At the focus of two of the
telescopes is a Gas Imaging Spectrometer
(GIS),
while a Solid-state Imaging Spectrometer
(SIS)
is at the focus of the other two. ASCA has provided recent evidence that
high
energy cosmic rays are formed in the expanding gas from a supernova.
During ASCA's three years of operation, it has also yielded valuable data
on quasars,
supernova remnants,
dwarf novae,
pulsars,
clusters of galaxies, and the mysterious
X-ray background
radiation that appears to come from all directions.
APOD: December 3, 1995 - An X-ray Hot Supernova in M81
Explanation:
In 1993, a star in the galaxy
M81 exploded.
Above is a picture of the hot material ejected by this
supernova explosion.
The picture was taken in
X-rays with the
Advanced
Satellite for Cosmology and Astrophysics
(ASCA).
Since M81 is a relatively nearby galaxy, it can be
examined in close detail by observatories on or near the
Earth. Since the
Earth's atmosphere protects the surface from
interstellar X-radiation, the
above
photo was taken from space. Studying
the nature and distribution of the X-rays has allowed astronomers to
determine the composition and temperature of the expanding supernova gas.
APOD: October 27, 1995 - The Tarantula and the Supernova
Explanation:
In this close-up of the Large Magellanic Cloud,
the spidery looking nebula on the left is fittingly known as
as the Tarantula nebula. It is an
emission nebula
surrounding a cluster of hot, young stars
called the 30 Doradus super cluster. This
cluster may contain the most massive stars known (about 50 times
the mass of the Sun). Such massive stars put out
more than 100 times as much energy as our Sun.
The bright "star" (lower right) is actually
Supernova 1987a
and is a harbinger of things to come for the stars
within the Tarantula. Massive stars
burn their nuclear fuel at drastically enhanced rates to support
their high energy output. As a result their lives
last only a few million years compared to the Sun's few billions of years.
They end in a spectacular death explosion, a
supernova,
like the star which exploded in 1987 as seen above.
Supernovae may leave behind imploded stellar cores which
form neutron stars or
black holes.
APOD: July 18, 1995 - Cygnus Loop Supernova Shockwave
Explanation:
15,000 years ago a star in the constellation of Cygnus exploded. This picture
shows a portion of a shockwave from this
supernova explosion still expanding
past nearby stars. The collision of this gaseous shockwave with
a stationary gas cloud has heated the gas causing it to
glow in a spectacular array of colors, known as the Cygnus Loop.
This picture was taken with
the Wide Field and Planetary Camera 2 on board the
Hubble Space Telescope.
APOD: June 21, 1995 - Supernova 1987a Aftermath
Explanation:
In 1987 a star in one of the Milky Way's satellite galaxies exploded. In
1994 the Hubble Space Telescope, in orbit around the earth, took a very
detailed picture of the remnants of this explosion. This picture, above,
showed unusual and unexpected rings,
and astronomers are not sure how they formed.