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: 2008 December 27 - Crab Pulsar Wind Nebula
Explanation:
The Crab Pulsar, a city-sized, magnetized
neutron star spinning 30 times a second,
lies at the center of
this
remarkable image from
the orbiting Chandra Observatory.
The deep x-ray image gives the first
clear view of
the convoluted boundaries of the Crab's pulsar wind nebula.
Like a
cosmic
dynamo the pulsar powers the x-ray
emission.
The pulsar's energy accelerates
charged particles, producing eerie, glowing x-ray jets directed
away from the poles and an intense wind in the equatorial direction.
Intriguing edges are created as the charged
particles stream away, eventually losing energy as they interact
with the pulsar's strong magnetic field.
With more mass than the Sun and the density of an
atomic nucleus,
the spinning pulsar itself is the collapsed core of a
massive star.
The stellar core collapse resulted in a supernova explosion that
was witnessed in
the year
1054.
This Chandra image spans just under 9 light-years at the Crab's
estimated distance of 6,000 light-years.
APOD: 2008 September 17 - MACSJ0025: Two Giant Galaxy Clusters
Collide
Explanation:
What happens when two of the largest objects in the universe collide?
No one was quite sure, but the answer is giving clues to the nature of
mysterious
dark matter.
In the case of
MACSJ0025.4-1222, two huge
clusters of
galaxies have been found slowly
colliding over hundreds of millions of years,
and the result has been imaged by both the
Hubble Space Telescope in
visible
light and the
Chandra Space Telescope in
X-ray light.
Once the above visible image was recorded, the location and
gravitational lens distortions
of more distant galaxies by the newly combined galaxy cluster
allowed astronomers to computationally determine what
happened to the clusters'
dark matter.
The result indicates that this huge collision has caused the dark matter
in the clusters to become partly separated from the normal matter,
confirming
earlier speculation.
In the
above
combined image, dark matter is shown as the diffuse purple hue, while
a smoothed depiction of the X-ray hot
normal matter
is shown in pink.
MACSJ0025 contains hundreds of galaxies, spans about three million
light years, and lies nearly six billion light years away
(redshift 0.59) toward the constellation of Monster Whale
(Cetus).
APOD: 2008 August 22 - Active Galaxy NGC 1275
Explanation:
Active galaxy NGC 1275
is the central, dominant member of the large and
relatively nearby
Perseus Cluster of Galaxies.
A prodigious source of
x-rays
and
radio
emission, NGC 1275 accretes
matter as entire galaxies fall into it, ultimately
feeding a supermassive black hole at the galaxy's core.
This stunning
visible
light image from the Hubble Space Telescope
shows galactic debris
and filaments of glowing gas,
some up to 20,000 light-years long.
The filaments persist in NGC 1275, even though
the turmoil of galactic collisions should destroy them.
What keeps the filaments together?
Recent work
indicates that the structures, pushed out
from the galaxy's center by the black hole's activity, are
held together by magnetic fields.
To
add x-ray data
from the Chandra Observatory and radio data from
the Very Large Array
to the Hubble image, just slide
your cursor over the picture.
In the resulting composite, x-rays highlight the
shells of hot gas
surrounding the center of the galaxy, with radio emission filling
giant bubble-shaped cavities.
Also known as Perseus A,
NGC 1275
spans over 100,000 light years and
lies about 230 million light years away.
APOD: 2008 August 4 - X-Rays from the Cat's Eye Nebula
Explanation:
Haunting patterns within planetary nebula
NGC 6543
readily suggest its popular moniker -- the
Cat's Eye nebula.
Starting in 1995, stunning false-color optical images
from the Hubble
Space Telescope detailed the swirls of this
glowing nebula, known to
be the gaseous shroud expelled from a dying
sun-like
star about 3,000 light-years from Earth.
This composite picture
combines the latest Hubble optical image of the Cat's Eye with new x-ray data from the
orbiting Chandra Observatory and reveals
surprisingly intense x-ray emission indicating the presence
of extremely hot gas.
X-ray emission is shown as blue-purple hues superimposed on the nebula's center.
The nebula's central star itself is clearly immersed in
the multimillion degree, x-ray emitting gas.
Other pockets of x-ray hot gas seem to be bordered by cooler
gas emitting strongly at optical wavelengths, a clear indication
that expanding hot gas is sculpting the
visible Cat's Eye
filaments and structures.
Gazing into the Cat's Eye, astronomers see
the fate of our sun,
destined to enter its own
planetary nebula phase
of evolution ... in about
5 billion
years.
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 June 27 - M81: Feeding a Black Hole
Explanation:
This impressive
color composite
shows spiral galaxy M81 across the
electromagnetic spectrum.
It combines X-ray data (blue) from the
Chandra
Observatory,
infrared data (pink) from the
Spitzer Space Telescope, and
an ultraviolet image (purple) from the
GALEX satellite,
with a visible light (green)
Hubble image.
The inset highlights X-rays from some of M81's black holes,
including
black
holes in binary star systems with about
10 times the mass of the sun, as well as the central,
supermassive black hole of over 70 million
solar masses.
Comparing computer models of the giant black hole's energy
output to the
multiwavelength data
suggests that feeding that
monster
is relatively simple -- energy and radiation is generated
as material in the central region swirls inwards forming an
accretion disk.
In fact, the process otherwise appears to be just like the
accretion process feeding M81's stellar mass black holes,
even though the central black hole is millions of times more massive.
M81 itself is about
70,000 light-years across and only 12 million
light-years away in the northern constellation
Ursa Major.
APOD: 2008 April 27 - The Galactic Center Radio Arc
Explanation:
What causes this unusual structure near the center of our Galaxy?
The long parallel rays slanting across the top of the
above radio image are known collectively as the
Galactic Center Radio Arc and jut straight out from the
Galactic plane.
The Radio Arc is connected to the
Galactic center
by strange curving filaments known as the
Arches.
The bright radio structure at the bottom right likely surrounds a
black hole at the
Galactic center and is known as
Sagittarius A*.
One origin hypothesis holds that the
Radio Arc and the Arches have their geometry
because they contain hot
plasma flowing along lines of constant
magnetic field.
Images from the
Chandra X-ray Observatory
appear to show this
plasma colliding with a nearby cloud of cold gas.
APOD: 2008 February 13 - Elliptical Galaxy NGC 1132
Explanation:
NGC 1132 is one smooth galaxy -- but how did it form?
As an
elliptical galaxy,
NGC 1132 has little dust and gas, and few stars have formed in it recently.
Although many elliptical galaxies are in clusters of galaxies, NGC 1132
appears as a large, isolated galaxy toward the constellation of
the River (Eridanus).
To probe the history of this intriguing trillion-star ball, astronomers imaged
NGC 1132 in both
visible light with the
Hubble Space Telescope and
X-ray light with the
Chandra X-ray Observatory.
In this composite false-color image, visible light is white,
while the X-ray light is blue and indicates the unusual
presence of very hot gas.
The X-ray light also likely traces out the location of
dark
matter.
One progenitor hypothesis is that NGC 1132 is the result of a series of
galaxy mergers in what once was a small
group of galaxies.
NGC 1132 is over 300 million light years away, so the light we see
from it today left before
dinosaurs
roamed the Earth.
Many
fascinating background galaxies
can be seen far in the distance.
APOD: 2008 January 31 - Young Star Cluster Westerlund 2
Explanation:
Dusty stellar nursery
RCW 49 surrounds young star cluster
Westerlund 2 in this remarkable composite skyscape
from beyond the visible
spectrum of light.
Infrared
data from the Spitzer Space Telescope is shown in
black and white, complimenting the Chandra
X-ray
image data (in false color) of the hot energetic stars
within the cluster's central region.
Looking toward the
grand
southern constellation
Centaurus, both
views
reveal stars and
structures hidden from optical telescopes by obscuring dust.
Westerlund 2
itself is a mere 2 million years old or
less, and contains some of our galaxy's most luminous, massive
and therefore
short-lived stars.
The infrared signatures
of proto-planetary disks have also been
identified in the intense star forming region.
At the cluster's estimated distance of 20,000 light-years,
the square marking the Chandra field of view would be
about 50 light-years on a side.
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: 2008 January 10 - Active Galaxy Centaurus A
Explanation:
A mere 11 million light-years away,
Centaurus A is a giant elliptical
galaxy - the closest active galaxy to Earth.
This remarkable
composite view of the galaxy
combines
image data
from the x-ray (
Chandra),
optical(ESO), and
radio(VLA)
regimes.
Centaurus A's central region
is a jumble of gas, dust, and stars
in optical light,
but both radio and x-ray telescopes trace a
remarkable jet of
high-energy particles streaming from the galaxy's core.
The cosmic
particle accelerator's
power source is a
black
hole with about 10 million times the mass of the
Sun coincident with the x-ray bright spot at the galaxy's center.
Blasting out from the active galactic nucleus toward the upper left,
the energetic jet extends about 13,000 light-years.
A shorter jet extends from the nucleus in the opposite direction.
Other x-ray bright spots
in
the field are binary star systems with neutron stars or stellar mass
black holes.
Active galaxy Centaurus A is likely the result of a
merger with
a spiral galaxy some 100 million years ago.
APOD: 2007 October 6 - X-Ray Stars of Orion
Explanation:
The stars of Orion shine brightly
in visible light in planet Earth's night sky.
The
constellation harbors the closest large stellar nursery,
the Great Nebula of Orion,
a mere 1,500 light-years away.
In fact, the apparently bright clump of stars near the center
of this false color Chandra
x-ray telescope picture
are the massive stars of
the Trapezium - the
young star cluster which powers much of the nebula's
visible-light glow.
The stars shown
in blue and orange are young sun-like stars; prodigious sources
of x-rays thought to be produced in hot
stellar coronae and
surface flares in a young star's strong
magnetic field.
Our middle-aged
Sun itself was
probably thousands of times
brighter in x-rays when, like
the
Trapezium stars, it was
only a few million years old.
The
x-ray image
spans about 2.5 light-years
across the central region of the Orion Nebula.
APOD: 2007 September 21 - Coronet in the Southern Crown
Explanation:
X-rays from
young stars and
infrared light
from stars and cosmic dust are combined in this false color image
of a star-forming region in Corona Australis,
the Southern Crown.
The small star grouping is
fittingly known as the
Coronet Cluster.
A mere 420 light-years distant, the
Coronet
Cluster offers
a relatively close-up view of stars and protostars
evolving with a wide range of masses.
The observations suggest that energetic
x-rays come from the
hot, extended stellar atmospheres or
coronae of the
Coronet stars.
The tantalizing multi-wavelength view spans about 2 light-years
and was produced using data from the orbiting
Chandra
Observatory (x-ray) and the
Spitzer
Space Telescope (infrared).
APOD: 2007 August 20 - Cluster Crash Illuminates Dark Matter Conundrum
Explanation:
Huge clusters of galaxies are surely colliding in Abell 520 but astrophysicists aren't sure why the dark matter is becoming separated from the normal matter.
The dark matter
in the above multi-wavelength image
is shown in false blue, determined by carefully detailing how the
cluster distorts light
emitted by more distant galaxies.
Very hot gas, a form of normal matter, is shown in false red, determined by the
X-rays
detected by the Earth-orbiting
Chandra X-ray Observatory.
Individual galaxies dominated by
normal matter appear yellowish or white.
Conventional wisdom holds that dark matter and normal matter are attracted the same gravitationally, and so should be distributed the same in
Abell 520.
Inspection of the
above image,
however, shows a surprising a lack of a concentration of
visible galaxies along the dark matter.
One hypothetical answer is that the discrepancy is caused by the
large galaxies
undergoing some sort of conventional gravitational slingshots.
A more controversial hypothesis holds that the dark matter is colliding with itself in some non-gravitational way that has never been seen before.
Further simulations and study of this cluster may resolve this scientific conundrum.
APOD: 2007 May 29 - Bright Spiral Galaxy M81 from Hubble
Explanation:
The Hubble Space Telescope has resolved individual stars
in a spectacular new image of nearby spiral galaxy M81.
The feat is similar to
Edwin Hubble's
historic images with the Mt. Wilson 100-inch Hooker Telescope in the 1920s that
resolved stars in neighboring galaxy
M31.
Edwin Hubble was able to use individual
Cepheid variable stars to show that M31 was not
nearby swirling gas but rather an
entire galaxy
like our
Milky Way Galaxy.
This above image in
visible light
taken by the
Hubble Space Telescope
is being used in conjunction with
images being taken in
ultraviolet by
Galex,
infrared by
Spitzer, and
X-rays with
Chandra
to study how stars have formed and died over the history M81.
Light takes about 12 million
years to reach us from M81.
M81
is visible with binoculars toward the constellation of the Great Bear
(Ursa Major).
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 May 5 - Sombrero Galaxy Across the Spectrum
Explanation:
Appropriately
famous for its broad ring of obscuring dust and
hat-like appearance, the Sombrero Galaxy (aka
spiral galaxy M104)
is featured in this
unique
composite view
that spans the
electromagnetic spectrum, from three major
space-based observatories.
Exploring the Sombrero's high-energy x-ray emission (blue), the
Chandra
contribution highlights the pervasive,
tenuous, hot gas that extends some 60,000 light-years from
the galaxy's center.
Hubble's optical
view (green) shows the more familiar emission from
the Sombrero's population of stars, seen from a nearly
edge-on
perspective and noticeably bulging at the galaxy's bright core.
The broad ring of dust that blocks light in other bands, glows in the
infrared contribution (red) from the
Spitzer Space Telescope.
The Sombrero Galaxy is about 28 million light-years away, near
the southern edge of the extensive
Virgo
cluster of galaxies.
APOD: 2007 March 14 - Barred Spiral Galaxy M95
Explanation:
Why do some spiral galaxies have a ring around the center?
First and foremost,
M95 is one of the
closer examples of a big and beautiful barred
spiral galaxy.
Visible in the
above recent image from the
CFHT telescope in
Hawaii,
USA, are sprawling
spiral arms delineate by
open clusters of bright blue stars, lanes of
dark dust, the diffuse glow of billions of faint stars,
and a short bar across the galaxy center.
What intrigues many astronomers, however, is the circumnuclear
ring around the galaxy center visible just outside the
central bar.
Recent images by the
Chandra X-ray Observatory have shown that
X-ray light
surrounding the ring is likely emission from recent
supernovas.
Although the long term stability of the ring remains a
topic of research,
recent observations indicate its present brightness is at least enhanced by
transient bursts of star formation.
M95,
also known as NGC 3351, spans about 50,000
light-years and can be seen with a small telescope toward the constellation of the Lion
(Leo).
APOD: 2007 February 24- X-rays and the Eagle Nebula
Explanation:
The premier Chandra X-ray Observatory
images of M16,
the Eagle Nebula, show many bright x-ray sources
in the region.
Most of the
x-ray
sources are energetic young stars.
They are seen here as colored spots superimposed on the Hubble's
well-known optical view of M16's light-year long
Pillars of Creation.
For example, a blue source
near
the tip of the large pillar at
the upper left is estimated to be an embedded young star
4 or 5 times as massive
as the Sun.
Still, most of the x-ray sources are not coincident
with the pillars themselves, indicating that embedded stars are
not common in the dusty structures.
The mostly empty pillars are thought to be an
indication that
star formation actually peaked millions of years ago
within
the Eagle
Nebula.
APOD: 2007 February 18 - M16: Pillars of Creation
Explanation:
It has become one of the most famous images of modern times.
This image, taken with the Hubble Space Telescope in 1995, shows evaporating gaseous globules (EGGs)
emerging from pillars of molecular
hydrogen gas and
dust.
The giant pillars are
light years in length
and are so dense that interior gas contracts gravitationally to form stars.
At each pillars' end,
the intense radiation of bright young stars
causes low density material to boil away, leaving
stellar nurseries of dense
EGGs exposed.
The Eagle Nebula, associated with the
open star cluster
M16, lies about 7000
light years away.
The pillars of creation were
imaged recently by the orbiting
Chandra X-ray Observatory, and it was found that most EGGS are not strong emitters of
X-rays.
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: 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 10 - Galactic Center Star Clusters
Explanation:
If you had
x-ray
vision, the central regions
of our Galaxy would not be hidden from
view by cosmic dust clouds.
Instead,
the Milky Way
toward Sagittarius might look something
like this.
Pleasing to look at, the gorgeous false-color representation of
x-ray data
from the Chandra Observatory shows
high energies in blue, medium in green,
and low energy x-rays in red.
The
mosaic spans about 130 light-years at the 26,000 light-year
distance of the Galactic Center.
It reveals massive, x-ray emitting star clusters
in a crowded environment.
In particular,
the Galactic Center cluster and the enormous
black hole
Sagittarius A* are within the bright region near the
bottom.
Two other star clusters, the Arches,
and the Quintuplet
lie near the top.
Cluster interactions with dense molecular clouds in the region
may produce some of the diffuse emission detected in
the Chandra
x-ray view.
APOD: 2006 July 29 - The Swarm
Explanation:
What do you
call a group of black
holes ... a flock, a brace, a swarm?
Monitoring a region around the
center of our Galaxy,
astronomers have indeed found
evidence for a surprisingly large number of
variable x-ray sources - likely black holes or neutron stars in
binary star systems - swarming
around the Milky Way's
own central supermassive black hole.
Chandra Observatory combined
x-ray image data from their monitoring
program
is shown above,
with four variable sources circled and labeled A-D.
While four sources may not make a swarm,
these all lie
within only three light-years of the central supermassive black
hole known as
Sgr A* (the bright source just above C).
Their detection
implies that a much larger concentration of
black hole systems is present.
Repeated gravitational interactions with other stars are
thought to cause the
black hole systems to spiral inward
toward the Galactic Center region.
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 July 22 - Mira: The Wonderful Star
Explanation:
To seventeenth century astronomers,
Omicron
Ceti or
Mira was
known as a wonderful star - a star whose brightness could change
dramatically in the course of about 11 months.
Modern astronomers now recognize an entire class of long period
Mira-type variables as cool,
pulsating, red giant stars, 700 or so times the diameter of the Sun.
Only 420 light-years away,
red
giant Mira (Mira A, right) itself
co-orbits with a companion star, a small white dwarf (Mira B).
Mira B is surrounded by a disk of material drawn from the pulsating
giant and in such a double star system, the white dwarf star's
hot accretion disk
is expected to produce
some x-rays.
But this sharp,
false-color image from the Chandra Observatory also
captures the cool giant star strongly
flaring at
x-ray energies, clearly
separated from the x-ray emission of its companion's accretion disk.
Placing your cursor over the Chandra x-ray image of Mira will reveal
an artist's vision of this still wonderful
interacting binary star system.
APOD: 2006 July 1 - Wind from a Black Hole
Explanation:
Binary star system
GRO J1655-40
consists of a relatively normal star about twice as massive as the Sun
co-orbiting with a black hole of about seven
solar masses.
This striking
artist's
vision of the exotic binary
system helps visualize matter drawn from the normal star by
gravity and swirling toward the black hole.
But it also includes a wind of material escaping from the black hole's
accretion disk.
In fact, astronomers
now argue
that Chandra Observatory x-ray data
indicate a high-speed wind is being driven from this system's
disk by magnetic forces.
Internal magnetic fields also help drive material in the swirling
disk into the
black hole itself.
If you had
x-ray
eyes as good as Chandra's, you could find
GRO J1655-40 about 11,000 light-years away in the constellation
Scorpius.
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: 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 January 18 - Cartwheel Of Fortune
Explanation:
By chance, a collision of two galaxies has created a surprisingly
recognizable shape on a cosmic scale -
The Cartwheel Galaxy.
The Cartwheel is part of a group of galaxies about 400 million
light years away in the
constellation
Sculptor
(two smaller galaxies in the group are visible below and left).
Its rim is an immense ring-like structure over 100,000 light
years in diameter, composed of star forming regions filled with
extremely bright, massive stars.
When galaxies collide they
pass through
each other, their individual stars do not come into contact.
However, this ring-like shape is the result of
gravitational
disruption caused by a smaller galaxy
passing through a large one, compressing the interstellar gas and
dust and causing a star formation wave to move out
like a ripple across the surface of a pond.
This
false-color composite image of the
Cartwheel Galaxy is from space-based observatories.
The Chandra X-ray Observatory
data is in purple,
the Galaxy
Evolution Explorer ultraviolet view is in blue,
the Hubble Space Telescope
visible light picture is in green and
the Spitzer Space Telescope
infrared image is in red.
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 8 - X-Rays from the Perseus Cluster Core
Explanation:
The Perseus Cluster of thousands of galaxies,
250 million light-years distant, is
one of
the most massive objects
in
the Universe and the brightest galaxy cluster in the
x-ray sky.
At its core lies the giant
cannibal galaxy Perseus A
(NGC
1275), accreting matter as
gas and galaxies fall into it.
This deep
Chandra Observatory x-ray image spans about 300,000 light-years
across the galaxy cluster core.
It shows
remarkable details
of x-ray emission from the monster galaxy and
surrounding hot (30-70 million degrees C) cluster gas.
The bright central source is the supermassive
black
hole at the core of Perseus A itself.
Low density regions are seen as dark bubbles or voids,
believed to be generated by cyclic outbursts of activity
from the central black hole.
The activity creates pressure waves -
sound waves on a cosmic scale-
that ripple through the x-ray hot gas.
Dramatically, the blue-green wisps just above centre in the
false-color view are likely x-ray shadows of
the remains of a small galaxy falling into the burgeoning
Perseus A.
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 2 - X Ray Portrait of Trumpler 14
Explanation:
A wonder of planet Earth's southern sky, star cluster
Trumpler
14 lies about nine thousand light-years away in the
Carina
complex -- a rich star forming region at the
edge of a giant molecular cloud.
This false-color x-ray
portrait
of Trumpler 14 from
the orbiting Chandra Observatory spans over 40 light-years and
reveals
stunning details of a cluster with one of the highest
concentrations of massive stars in the Galaxy.
Profoundly affecting their environment,
the hot cluster stars are themselves a mere one million years old.
Energetic winds from the stars have
cleared out a cavity in
the dense cloud, filling it with shock heated,
x-ray
emitting gas.
Still to come, the next few million years will see these stellar
prodigies rapidly exhaust their nuclear fuel and explode in violent
supernovae, flooding their cosmic neighborhood with
gas enriched in heavy elements.
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 21 - X-Ray Stars of 47 Tuc
Explanation:
Visible light images
show the central region of globular
cluster 47
Tucanae is closely packed, with stars
less than a tenth of a light-year apart.
This Chandra false-color
x-ray view
of central 47 Tuc also shows the
cluster is a popular neighborhood for
x-ray stars,
many of which are "normal" stars
co-orbiting with extremely dense
neutron stars
-- stars with the mass of the Sun but
the diameter of Manhattan Island.
One of the most remarkable of these exotic
binary systems is
cataloged as 47 Tuc W, a bright source
near
the center of this image.
The system consists of a low mass star and a
a neutron star that spins once every 2.35
milliseconds.
Such neutron stars are known to radio astronomers
as millisecond pulsars, believed to be driven to such
rapid rotation by material falling from the normal star onto
its dense companion.
In fact, x-ray observations of the 47 Tuc W system
link this
spin-up mechanism observed to operate in other x-ray binary
stars with fast rotating millisecond
pulsars.
APOD: 2005 June 1 - White Dwarf Star Spiral
Explanation:
About 1,600 light-years away, in a
binary star system
fondly
known as J0806, two dense white dwarf stars
orbit each
other
once every 321 seconds.
Interpreting
x-ray data
from the Chandra
Observatory astronomers argue that the stars'
already impressively short orbital period is steadily getting
shorter as the stars spiral closer together.
Even though they are separated by about 80,000 kilometers
(the Earth-Moon distance is 400,000 kilometers)
the two stars are therefore destined to merge.
Depicted in this artist's vision,
the death spiral
of the remarkable J0806 system is
a consequence of Einstein's theory
of General Relativity that
predicts the white dwarf stars will lose
their orbital energy by generating
gravity waves.
In fact, J0806 could be one of the brightest sources of
gravitational waves in our galaxy, directly
detectable by future space-based
gravity wave instruments.
APOD: 2005 May 19 - X Ray Stars in the Orion Nebula
Explanation:
When our
middle-aged Sun
was just a few
million years old it was
thousands of times brighter
in
x-rays.
In fact, it was likely similar to some of the stars found
in this false-color x-ray composite of the Orion Nebula region
from the Chandra Observatory.
The image is
centered
on bright stars of the nebula's
Trapezium star cluster, and while
analyzing the
Chandra data
astronomers have now found examples of young,
sun-like stars producing intense
x-ray flares.
It sounds dangerous, but the situation may actually
favor the formation of
hospitable
planetary systems like our own.
Energetic flares can produce turbulence in the
planet-forming disks
surrounding the stars -
preventing rocky earth-like planets from spiraling uncomfortably
close to and even
falling into
their active, young parent stars.
About 1,500 light-years away, the
Orion Nebula is the closest
large stellar nursery.
At that distance, this Chandra image spans about 10 light-years.
APOD: 2005 May 5 - Mira: The Wonderful Star
Explanation:
To seventeenth century astronomers,
Omicron
Ceti or
Mira was
known as a wonderful star - a star whose brightness could change
dramatically in the course of about 11 months.
Modern astronomers now recognize an entire class of long period
Mira-type variables as cool,
pulsating, red giant stars, 700 or so times the diameter of the Sun.
Only 420 light-years away,
red
giant Mira (Mira A, right) itself
co-orbits with a companion star, a small white dwarf (Mira B).
Mira B is surrounded by a disk of material drawn from the pulsating
giant and in such a double star system, the white dwarf star's
hot accretion disk
is expected to produce
some x-rays.
But this sharp,
false-color image from the Chandra Observatory also
captures the cool giant star strongly
flaring at
x-ray energies, clearly
separated from the x-ray emission of its companion's accretion disk.
Placing your cursor over the Chandra x-ray image of Mira will reveal
an artist's vision of this still wonderful
interacting binary star system.
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 9 - Inside The Elephant's Trunk
Explanation:
In December of 2003, the world saw
spectacular first images
from the
Spitzer
Space Telescope,
including this penetrating interior view of an otherwise
opaque dark globule known as the
Elephant's Trunk Nebula.
Seen in a composite of infrared image data
recorded by
Spitzer's instruments, the intriguing region is
embedded within
the glowing emission nebula IC 1396 at a distance of 2,450
light-years toward the constellation Cepheus.
Previously undiscovered protostars
hidden by dust at optical wavelengths
appear as bright reddish objects within the
globule.
Shown in false-color,
winding filaments of infrared emission
span about 12 light-years and are due to dust,
molecular hydrogen gas, and complex molecules called
polycyclic aromatic hydrocarbons
or PAHs.
The
Spitzer Space Telescope was
formerly known as the Space
Infrared Telescope Facility (SIRTF) and
is presently exploring
the Universe at infrared
wavelengths.
Spitzer follows the Hubble Space Telescope,
the Compton Gamma-ray Observatory, and the Chandra X-ray Observatory
as the final element in NASA's space-borne
Great Observatories
Program.
APOD: 2005 April 3 - The Galactic Center Radio Arc
Explanation:
What causes this unusual structure near the center of our Galaxy?
The long parallel rays slanting across the top of the
above radio image are known collectively as the
Galactic Center Radio Arc and jut straight out from the
Galactic plane.
The Radio Arc is connected to the
Galactic center
by strange curving filaments known as the Arches.
The bright radio structure at the bottom right
likely surrounds a
black hole at the
Galactic center and is known as
Sagittarius A*.
One origin hypothesis holds that the
Radio Arc and the Arches have their geometry
because they contain hot
plasma flowing along lines of constant
magnetic field.
Recent images from the
Chandra X-ray Observatory
appear to show this
plasma colliding with a nearby cloud of cold gas.
APOD: 2005 March 30 - ULXs in M74
Explanation:
In visual appearance, M74 is a
nearly perfect face-on spiral
galaxy, about 30 million light-years away toward the
constellation Pisces.
The red blotches seen in
this
composite view are ultraluminous
x-ray sources (ULXs) mapped by the
Chandra X-ray Observatory.
The ULXs are so called because they actually do radiate 10 to
1,000 times more x-ray power than "ordinary"
x-ray binary stars,
which harbor a neutron star or
stellar mass
black hole.
In fact,
watching
these ULXs change their
x-ray brightness over periods of 2 hours or so, astronomers
conclude that ULXs could well be
intermediate mass black holes --
black holes with
masses 10,000 times or so greater than the Sun, but still much less
than the million solar mass black holes which
lurk in the centers
of large spiral galaxies.
How did these intermediate mass black holes get there?
One intriguing suggestion is that they are left over from
the cores of much smaller galaxies that are
merging with
spiral galaxy M74.
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 January 28 - The Swarm
Explanation:
What do you
call a group of black
holes ... a flock, a brace, a swarm?
Monitoring a region around the
center of our Galaxy,
astronomers have indeed found
evidence for a surprisingly large number of
variable x-ray sources - likely black holes or neutron stars in
binary star systems - swarming
around the Milky Way's own
central supermassive black hole.
Chandra Observatory combined
x-ray image data from their monitoring
program
is shown above,
with four variable sources circled and labeled A-D.
While four sources may not make a swarm,
these all lie
within only three light-years of the central supermassive black
hole known as
Sgr A* (the bright source just above C).
Their detection
implies that a much larger concentration of
black hole systems is present.
Repeated gravitational interactions with other stars are
thought to cause the
black hole systems to spiral inward
toward the Galactic Center region.
APOD: 2005 January 8 - 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: 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 November 6 - X-Rays from the Galactic Core
Explanation:
Using the orbiting
Chandra
X-ray Observatory, astronomers have taken
this long look at the core of our
Milky Way galaxy, some 26,000 light-years away.
The spectacular false-color view spans about 130 light-years.
It reveals an energetic region
rich in x-ray sources and high-lighted by the
central source, Sagittarius A*, known
to be a supermassive black hole
with 3 million times the
mass of
the Sun.
Given its tremendous mass, Sagittarius A* is amazingly faint in x-rays
in comparison to central black holes observed in
distant galaxies,
even during its frequent x-ray flares.
This suggests that this supermassive black hole has been
starved
by a lack of infalling material.
In fact, the sharp Chandra image shows clouds of multi-million
degree gas dozens of light-years across flanking
(upper right and lower left) the
central
region -- evidence that violent events have
cleared much material from
the vicinity of the black hole.
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 24 - Fornax Cluster in Motion
Explanation:
Reminiscent of popular images of the
lovely Pleiades star
cluster that lies within our own Milky Way Galaxy, this
false-color
x-ray view actually explores the center of a much
more extended cosmic family -- the
Fornax cluster of
galaxies some 65 million light-years away.
Spanning nearly 900,000 light-years, the
Chandra Observatory
composite image reveals high-energy emission from several
giant galaxies near the Fornax cluster center and an immense,
diffuse cloud of x-ray emitting hot gas.
On the whole, the hot cluster gas seems to be
trailing toward the upper left in this view.
As a result,
astronomers
surmise that the Fornax cluster
core is moving toward the lower right, encountering
an intergalactic headwind as it sweeps through a larger,
less dense cloud of material.
In fact, along with another visible galaxy grouping at the
outskirts of the cluster, the Fornax cluster core galaxies
seem to be moving toward a common point,
attracted by the dominating gravity of
unseen structures of
dark
matter in the region.
APOD: 2004 September 8 - Molecular Torus Surrounds Black Hole
Explanation:
Why do some black hole surroundings appear brighter than others?
In the centers of
active galaxies, supermassive
black holes at least
thousands of times the mass of our
Sun dominate.
Many, called
Seyfert Type I, are very bright in visible light.
Others, called Seyfert Type II, are rather dim.
The difference might be caused by some
black holes accreting
much more matter than others.
Alternatively, the black holes in the center of
Seyfert
Type II galaxies might be obscured by a surrounding
torus.
To help choose between these competing hypotheses,
the nearby Seyfert II galaxy
NGC 4388 has been observed in
X-ray light recently by many recent Earth-orbiting
X-ray observatories, including
CGRO,
SIGMA,
BeppoSAX,
INTEGRAL,
Chandra, and
XMM-Newton.
Recent data
from INTEGRAL and XMM-Newton have
found that the X-ray flux in some X-ray colors varies rapidly,
while flux in other X-ray colors is quite steady.
The constant flux and apparent absorption of very
specific X-ray colors by cool
iron together
give evidence that the central black hole in NGC 4388 is seen through a
thick torus composed of
molecular gas and dust.
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 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 March 12 - X-Ray Saturn
Explanation:
Above, the ringed planet
Saturn
shines in x-rays.
Otherwise beyond the range of human vision, the eerie
x-ray view was created by overlaying a computer
generated
outline of the gas giant's disk and ring system on a false-color
picture of smoothed,
reconstructed
x-ray data
from the orbiting Chandra Observatory.
The data represent the first clear detection
of Saturn's disk
at x-ray energies and held some surprises for
researchers.
For starters, the x-rays seem concentrated near the planet's
equator rather than the poles, in marked contrast to
observations of Jupiter, the only
other gas giant seen at such high energies.
And while Saturn's high energy emission is found to be consistent
with the reflection of x-rays
from the Sun, the intensity of the
reflected x-rays was also found to be unusually strong.
Outside the planet's disk, only a faint suggestion of x-rays from
Saturn's magnificent
ring system
is visible at the left.
APOD: 2004 February 26 - Galaxy Cluster in the Early Universe
Explanation:
Long before medieval alchemists dreamed of transmuting
base metals to gold, stellar furnaces
in this massive cluster
of galaxies - cataloged as RDCS 1252.9-2927 - had transformed
light
elements into heavy ones.
In the false-color
composite image individual cluster galaxies can
be seen at optical and near-infrared wavelengths, shown
in red, yellow, and green colors.
X-ray
data (in purple) reveal the hot
intracluster gas, enriched
in heavy elements.
Attracting the attention of astronomers using the orbiting
Chandra and
XMM-Newton x-ray telescopes, as well as the
Hubble Space Telescope
and ground based VLT,
the galaxy cluster lies nearly 9
billion light-years away ...
and so existed at a time when the Universe was less
than 5 billion years old.
A measured mass of more than 200
trillion Suns makes this galaxy cluster
the most massive object ever found when the Universe was so young.
The cluster
elemental abundances are consistent with the idea
that most heavy elements were synthesized early on by massive stars,
but current theories suggest that such a massive cluster should
be rare in the early Universe.
APOD: 2004 February 3 - X-Rays From Antennae Galaxies
Explanation:
A bevy of
black holes and
neutron stars
shine as bright, point-like
sources against bubbles of
million degree gas in this
false-color
x-ray image from the
orbiting Chandra Observatory.
The striking picture spans about 80 thousand light-years across the
central regions of two
galaxies, NGC 4038 and NGC 4039, locked in a titanic collision
some 60 million light-years away in the
constellation Corvus.
In visible light images, long, luminous,
tendril-like structures emanating
from the wreckage lend the pair their
popular moniker, the Antennae Galaxies.
Galactic collisions are now thought to be
fairly common, but when
they happen individual stars rarely collide.
Instead gas and dust clouds merge and compress, triggering furious
bursts of massive star formation with
thousands of resulting supernovae.
The exploding stars litter the scene with bubbles of shocked gas
enriched
in heavy elements, and collapsed stellar cores.
Transfixed by this cosmic accident
astronomers watch and are beginning
to appreciate the
collision-driven evolution
of galaxies, not unlike our own.
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 December 19 - Inside The Elephant's Trunk
Explanation:
Spectacular first images
from the newly christened
Spitzer Space Telescope
include this penetrating interior view of an otherwise
opaque dark globule known as the
Elephant's Trunk Nebula.
Seen in a composite of infrared image data
recorded by
Spitzer's instruments, the intriguing region is
embedded within
the glowing emission nebula IC 1396 at a distance of 2,450
light-years toward the constellation Cepheus.
Previously undiscovered protostars
hidden by dust at optical wavelengths
appear as bright reddish objects within the
globule.
Shown in false-color,
winding filaments of infrared emission
span about 12 light-years and are due to dust,
molecular hydrogen gas, and complex molecules called
polycyclic aromatic hydrocarbons
or PAHs.
The
Spitzer Space Telescope was
formerly known as the Space
Infrared Telescope Facility (SIRTF) and
is designed to explore
the Universe at infrared
wavelengths.
Spitzer follows the Hubble Space Telescope,
the Compton Gamma-ray Observatory, and the Chandra X-ray Observatory
as the final element in NASA's space-borne
Great Observatories Program.
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 October 4 - X-Ray Moon
Explanation:
This x-ray image of the Moon
was made by the orbiting
ROSAT
(Röntgensatellit) Observatory in 1990.
In this digital picture, pixel brightness corresponds to x-ray intensity.
Consider the image in three parts:
the bright hemisphere of the x-ray moon,
the darker half of the moon,
and the x-ray sky background.
The bright lunar hemisphere shines
in x-rays because it scatters
x-rays emitted by the sun.
The background sky has an x-ray
glow in part due to
the myriad of distant, powerful active galaxies, unresolved
in the ROSAT picture but recently detected in Chandra Observatory
x-ray images.
But why isn't the dark half of the moon completely dark?
New
Chandra results also suggest that a few x-rays only seem
to come from the shadowed
lunar hemisphere.
Instead, they
originate in Earth's geocorona or
extended
atmosphere which surrounds the orbiting x-ray observatories.
APOD: 2003 September 12 - A Note on the Perseus Cluster
Explanation:
A truly enormous collection of thousands of galaxies, the
Perseus Cluster - like other
large galaxy clusters - is
filled with hot, x-ray emitting gas.
The x-ray hot gas
(not the individual galaxies) appears
in the left panel above, a false color
image
from the Chandra Observatory.
The bright central source flanked by two
dark cavities is
the cluster's supermassive black hole.
At right, the panel shows the
x-ray image
data specially processed
to enhance contrasts and reveals a strikingly regular
pattern of pressure waves
rippling through
the hot gas.
In other words,
sound
waves, likely generated by bursts of
activity from the black hole, are ringing through the
Perseus Galaxy Cluster.
Astronomers infer that these previously unknown sound waves are a
source of energy which keeps the cluster gas so hot.
So what note is the Perseus Cluster playing?
Estimates of the distance between the wave peaks and sound speed
in the cluster gas suggests
the cosmic note is about 57 octaves below B-flat above middle C.
APOD: 2003 September 5 - SIRTF Streak
Explanation:
Streaking skyward, a
Boeing Delta 2-Heavy rocket carries NASA's
Space InfraRed
Telescope Facility (SIRTF) aloft during
the early morning hours of August 25th.
The dramatic scene was recorded in a time exposure from the pier
in Jetty Park at the northern end of Cocoa Beach, Florida,
about 2.5 miles from the Cape Canaveral launch site.
SIRTF (sounds like "sir tiff") will explore the distant
Universe in infrared light
as the fourth and final
satellite observatory in NASA's
Great Observatories Program.
The three other large astrophysics satellites were designed
for higher energies in the electromagnetic spectrum, with the
Hubble Space Telescope
operating near visible wavelengths, the
Compton Gamma Ray Observatory
instruments sensitive to gamma rays, and the
Chandra Observatory
detecting cosmic x-rays.
SIRTF has been launched into an
Earth-trailing
solar orbit to reduce its exposure to infrared radiation from
our fair planet.
Cooled by an on board supply of
liquid helium,
SIRTF's infrared detectors will operate at near absolute zero
temperatures.
Presently, SIRTF's systems are undergoing a 90-day check out.
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 August 21 - X-Rays from M17
Explanation:
About 5,000
light-years
away, toward the constellation Sagittarius
and the center of our galaxy,
lies the bright star forming region
cataloged as M17.
In visible light, M17's bowed and hollowed-out appearance has resulted in
many popular names
like the Horseshoe, Swan, Omega, and Lobster
nebula.
But what has
sculpted this glowing gas cloud?
This
Chandra
Observatory image of x-rays from M17 provides a clue.
Many massive young stars are responsible for the pink
central region of the false-color
x-ray picture, their colliding
stellar winds producing the
multimillion
degree gas cloud
which extends ten or so light-years to the left.
When compared
with visible light images,
this x-ray hot cloud is partly surrounded by the nebula's cooler gas.
In fact, having carved out a central cavity
the hot gas seems to be flowing out of the horseshoe
shape like champagne from an uncorked bottle ...
suggesting yet another name for star forming
region M17.
APOD: 2003 August 12 - X-rays from Stephan s Quintet
Explanation:
Stephan's
Quintet is a picturesque but clearly troubled
grouping of galaxies about 300 million light-years away
toward the high-flying constellation
Pegasus.
Spanning over 200,000 light-years at that distance,
this
composite false-color image
illustrates the powerful nature of this
multiple
galaxy collision,
showing x-ray data from the
Chandra
Observatory in blue superposed on optical data in yellow.
The x-rays
from the central blue cloud running vertically
through the image are produced by
gas heated to millions of degrees by an energetic
shock on a cosmic scale.
The shock was likely the result of the interstellar gas
in the large spiral galaxy, seen immediately to the right
of the cloud,
colliding with the quintet's tenuous intergalactic gas
as this galaxy plunged through group's central regions.
In fact, over billions of years, repeated passages of the
group galaxies through the hot intergalactic
gas should progressively strip them of their own star
forming material.
In this view, the large spiral galaxy just seen peeking
above the bottom edge is an unrelated foreground galaxy
a mere 35 million light-years distant.
APOD: 2003 July 12 - X-Ray Milky Way
Explanation:
If you had x-ray vision,
the center regions
of our Galaxy would not be hidden from
view by the immense cosmic dust clouds
opaque to visible light.
Instead,
the Milky Way
toward Sagittarius might look something
like this stunning mosaic
of images from the orbiting
Chandra Observatory.
Pleasing to look at, the gorgeous false-color
representation of
the x-ray data shows
high energy x-rays in blue, medium energies in green,
and low energies in red.
Hundreds of white dwarf stars,
neutron stars, and black holes immersed in a
fog of multimillion-degree gas are included in the
x-ray vista.
Within the white patch at the image center lies
the Galaxy's central supermassive black hole.
Chandra's sharp
x-ray vision will likely lead to a new
appreciation of our Milky Way's most active neighborhood
and has already indicated that the hot gas itself may
have a temperature of a mere 10 million degrees Celsius
instead of 100 million degrees as previously thought.
The full mosaic is composed of 30 separate images and covers
a 900 by 400 light-year swath
at
the galactic center.
APOD: 2003 July 11 - NGC 1068 and the X-Ray Flashlight
Explanation:
At night,
tilting a flashlight up under your chin hides the
glowing bulb from the direct view of your friends.
Light from the bulb still reflects from your face though, and can
give you a startling appearance.
Spiral
Galaxy NGC 1068
may be playing a similar trick on a
cosmic scale,
hiding a central powerful source of x-rays -- likely a
supermassive black hole -- from direct view.
X-rays are
still scattered into our line-of-sight
though, by a dense torus of material surrounding the black hole.
The scenario is
supported by x-ray data from the
Chandra Observatory combined with a Hubble Space
Telescope optical image in
this
false-color composite picture.
Optical data in red shows spiral structure across NGC 1068's
inner 7 thousand light-years with the x-ray data overlaid in blue
and green.
A hot wind of gas streaming from the galaxy's core
is seen as the broad swath of x-ray emission while material
lit up
by the hidden black hole source is within the central
cloud of more intense x-rays.
Also well known
as M77, NGC 1068 lies a mere 50 million
light-years away toward the constellation Cetus.
APOD: 2003 July 5 - Centaurus A: X-Rays from an Active Galaxy
Explanation:
Its core hidden
from optical view by a thick lane of dust, the giant elliptical
galaxy
Centaurus A was among the first objects
observed by the orbiting Chandra X-ray Observatory.
Astronomers were not disappointed, as Centaurus A's
appearance in x-rays makes its classification as an
active galaxy easy to appreciate.
Perhaps the most striking feature of
this
Chandra false-color x-ray view
is the jet, 30,000 light-years long.
Blasting toward the upper left corner of the picture,
the jet
seems to arise from the galaxy's bright central x-ray source --
suspected of harboring a black hole with a million or so times
the mass of the Sun.
Centaurus A
is also seen to be teeming with other
individual x-ray sources and a pervasive, diffuse
x-ray glow.
Most of these individual sources are likely to be neutron stars
or solar mass black holes accreting material from their less
exotic binary companion stars.
The diffuse high-energy glow
represents gas throughout the galaxy
heated to temperatures of millions
of degrees C.
At 11 million light-years distant in the constellation
Centaurus,
Centaurus A (NGC 5128) is the closest
active galaxy.
APOD: 2003 July 3 - The Vela Pulsar's Dynamic Jet
Explanation:
The Vela pulsar is a neutron star born over 10,000 years ago
in a massive supernova explosion.
Above, false-color
x-ray images from the
Chandra
Observatory reveal details of this remnant pulsar's
x-ray bright nebula
along with emission from a spectacular jet of
high-energy particles.
In this time-lapse series
of pictures, the jet
seems to dance
around very much like an out-of-control firehose,
shooting along the pulsar's
direction of motion (toward the top right corner)
to a length of about half a light-year while
whipping back and forth at about half the speed of light.
Highly magnetized and spinning over 10 times a second,
the Vela pulsar is thought of as a
cosmic
high-voltage generator, powering the x-ray nebula and
dynamic cosmic jet.
A mere 800 light-years away the
pulsar itself is located near
the lower left corner in the four panels.
APOD: 2003 June 25 - Galaxies in the GOODS
Explanation:
This tantalizing view of galaxies scattered near and far is part of the
Hubble Space Telescope's
contribution
to the GOODS - the
Great Observatories Origins Deep Survey project.
The GOODS'
goal is to study
galaxy
formation and evolution over an unprecedent wide range of
cosmic
distances, therefore spanning
time from
the present to the early Universe.
Joined by the
Chandra
X-ray Observatory and soon by the anticipated
Space
Infrared Telescope Facility
along with major ground-based
observatories, the project expands greatly on the past
Hubble Deep Fields of regions in the northern constellation of
Ursa Major and southern constellation Tucana.
Across the
electromagnetic
spectrum, a sample of
large nearby galaxies,
like the interacting pair at the lower left above, will be compared with
distant younger
galaxies in a search for clues to the origins of
these lighthouses of the cosmos.
Preliminary results of the project confirm that the birth rate
of stars was higher in the past and that galaxies
have indeed been constructed from
the "bottom up", growing
from mergers and accretion of small infant galaxies to their
present day forms.
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 1 - The Energetic Jet from Centaurus A
Explanation:
The center of well-studied active galaxy
Centaurus A
is hidden from the view of optical
telescopes by a cosmic jumble of stars, gas, and dust.
But both radio and
x-ray
telescopes can trace the
remarkable jet
of high-energy particles streaming from the galaxy's core.
With Cen A's central region at the lower right,
this composite false-color image shows the
radio emission in red and x-rays in blue over
the inner 4,000 light-years of the jet.
One of the most detailed images of its kind,
the
picture shows how the x-ray
and radio emitting sites are related along the
jet, providing
a road map to understanding the energetic stream.
Extracting
its energy from a supermassive black hole at the
galaxy's center, the jet is confined to a relatively narrow angle
and seems to produce most of its x-rays (bluer colors) at the upper left,
farther from the core, where the jet begins to collide with
Centaurus A's
denser gas.
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 14 - The Heart in NGC 346
Explanation:
Yes, it's Valentine's Day (!) and
looking toward star cluster
NGC 346
in our neighboring galaxy
the Small
Magellanic Cloud, astronomers have noted
this heart-shaped cloud of hot, x-ray emitting gas
in the cluster's central region.
The false-color Chandra Observatory
x-ray image
also shows a strong
x-ray source just above the heart-shaped cloud which corresponds
to HD 5980, a remarkable, massive binary star system that lies within
the cluster.
HD 5980
has been known to undergo dramatic brightness variations,
in 1994 briefly outshining all other stars in the
Small Magellanic Cloud, and has been likened to
the luminous, eruptive variable star
Eta Carinae in our own Milky Way galaxy.
At about 100 light-years across,
NGC 346's
heart-shaped cloud is probably the result of an ancient
supernova explosion.
Alternatively it may
have been produced during past eruptions from the HD 5980 system, analogous
to the nebula associated with
Eta Carinae.
APOD: 2003 February 6 - X-Rays from M83
Explanation:
Bright and beautiful spiral galaxy
M83 lies a mere
twelve million light-years from Earth, toward the
headstrong constellation
Hydra.
Sweeping spiral arms, prominent in visible light images,
lend this galaxy its popular moniker --
the Southern Pinwheel.
In fact, the spiral arms are still apparent in this
Chandra Observatory false-color
x-ray image of M83,
traced by diffuse, hot,
x-ray emitting gas.
But more striking in the
x-ray
image is the galaxy's bright central
region.
The central emission likely represents even hotter gas
created by a sudden burst
of massive star formation.
Point-like neutron star and black hole x-ray
sources,
final stages in the life cycles of massive stars,
also show a
concentration near
the center of M83 and offer
further evidence for a burst of star formation
at this galaxy's core.
Light from this burst of star formation
would have first reached Earth some 20 million years ago.
APOD: 2003 January 16 - NGC 1700: Elliptical Galaxy and Rotating Disk
Explanation:
In spiral galaxies, majestic winding arms
of young stars and interstellar
gas and dust rotate
in a disk around a bulging galactic nucleus.
Elliptical
galaxies
seem to be simpler, randomly
swarming with old stars and lacking gas and dust.
So astronomers were
excited
to find that NGC 1700, a young elliptical
galaxy about 160 million light-years away, shows evidence for a
90,000 light-year wide rotating disk of multi-million
degree hot gas.
The evidence comes from data recorded by the
orbiting
Chandra Observatory, whose sharp
x-ray image of NGC 1700 is seen above.
Balancing gravity, the rotation of the
x-ray hot disk,
the largest of its type yet discovered, gives the galaxy
a pronounced boxy profile in this false-color picture.
Theories about
the origin of the disk suggest that NGC 1700 may be the result
of a cosmic scale galactic merger,
perhaps between a spiral and
elliptical galaxy.
NGC 1700 is just visible with small telescopes toward the
flowing constellation Eridanus.
APOD: 2003 January 8 - X-Rays from the Galactic Core
Explanation:
Using the orbiting
Chandra
X-ray Observatory, astronomers have taken
this long look at the core of our
Milky Way galaxy, some 26,000 light-years away.
The spectacular false-color view spans about 130 light-years.
It reveals an energetic region
rich in x-ray sources and
high-lighted by the
central source, Sagittarius A*, known
to be a supermassive black hole
with 3 million times the
mass of
the Sun.
Given its tremendous mass, Sagittarius A* is amazingly faint in x-rays
in comparison to central black holes observed in
distant galaxies,
even during its frequent x-ray flares.
This suggests that this supermassive black hole has been
starved
by a lack of infalling material.
In fact, the sharp Chandra image shows clouds of multi-million
degree gas dozens of light-years across flanking
(upper right and lower left) the
central
region -- evidence that violent events have
cleared much material from
the vicinity of the black hole.
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 November 28 - The Supermassive Black Holes of NGC 6240
Explanation:
The
Hubble optical image on the left shows
NGC 6240 in
the throes of a
titanic galaxy - galaxy collision 400 million light-years away.
As the cosmic catastrophe plays out, the merging galaxies spew forth
distorted tidal tails
of stars, gas, and dust and undergo
frantic bursts of star formation.
Using the orbiting
Chandra
Observatory's x-ray vision to peer within
the bright central regions of NGC 6240 astronomers
believe they have uncovered,
for
the first time, not one but
two enormous orbiting black holes, by
detecting the characteristic x-ray radiation from the interstellar debris
swirling toward them.
In the false-color close-up view at right,
the x-ray data clearly show
the black hole
sources (shaded blue) separated by about 3,000 light-years.
Einstein's theory of gravity predicts that such a pair of black holes
must spiral closer together, and
ultimately coalesce into a single,
even more massive black hole
after
several hundred million
years.
In the final moments the merging supermassive black holes will
produce an extremely powerful burst of
gravitational radiation.
APOD: 2002 November 24 - Hubble Floats Free
Explanation:
Why put observatories in space?
Most telescopes are on the ground.
On the ground, you can deploy a heavier telescope
and fix it more easily.
The trouble is that
Earth-bound telescopes
must look through the Earth's atmosphere.
First, the Earth's atmosphere
blocks out a broad range of the
electromagnetic spectrum, allowing
a narrow band of visible light to reach the surface.
Telescopes which explore the Universe using light
beyond the visible spectrum, such as those onboard the
Chandra X-ray Observatory
need to be carried above the absorbing atmosphere.
Second, the Earth's atmosphere blurs the light
it lets through.
The blurring is caused by varying density and
continual motion of air.
By orbiting above the Earth's atmosphere,
the Hubble Space Telescope,
pictured above,
can get clearer images.
In fact, even though HST
has a mirror 15 times smaller than large Earth-bound telescopes,
it can still resolve finer details.
A future large
optical telescope in space is
planned.
APOD: 2002 October 26 - Dark Matter, X-rays, and NGC 720
Explanation:
Elliptical galaxy NGC 720 is enveloped in a
cosmic cloud of x-ray emitting gas.
Seen in
this
false color image from the
Chandra
X-ray Observatory,
the extreme temperature of the gas - about 7 million degrees Celsius -
makes it impossible to confine the cloud to the vicinity of NGC 720 based
on the gravity of this galaxy's visible stars alone.
In fact, the x-ray cloud is taken as solid evidence for the
presence
of dark matter surrounding NGC 720 -- unseen material which has
gravitational influence that can keep the x-ray hot gas cloud
from escaping.
Chandra's remarkable vision clearly distinguishes the bright
point-like x-ray
sources from the diffuse cloud.
Astronomers can then use
the detailed shape
of the cloud to infer
the distribution of dark matter in NGC 720 and even test theories
about the fundamental nature of dark matter.
According to modern understanding, the mysterious
dark matter, whatever
it is, is by far the most common
form of matter in the Universe.
Galaxy NGC 720 lies about 80 million light-years distant
toward the constellation Cetus.
APOD: 2002 October 12 - Chandra Deep Field
Explanation:
Officially the
Chandra
Deep Field - South, this picture represents the deepest ever
x-ray image of the Universe.
One million seconds of accumulated exposure time with the orbiting
Chandra X-ray Observatory went in to its making.
Concentrating on a single, otherwise unremarkable patch
of sky in the constellation
Fornax,
this x-ray image corresponds to the
visible light Hubble Deep Field - South
released in 1998.
Chandra's view, color coded with low energies in red, medium in green,
and high-energy x-rays in blue, shows many faint sources of relatively
high-energy x-rays.
These are likely active galaxies feeding supermassive central
black holes
and large clusters of galaxies
at distances of up to 12 billion light-years.
The stunning picture supports
astronomers' ideas
of a youthful
universe in which massive black holes
were much more dominant than at present.
APOD: 2002 October 8 - The X-Ray Jets of XTE J1550
Explanation:
The motion of ultra-fast
jets shooting out from a candidate
black hole star system have now been documented
by observations from the orbiting
Chandra X-ray Observatory.
In 1998, X-ray source
XTE J1550-564 underwent a tremendous outburst.
Jets of material sent streaming into space at
near light-speed impacted existing gas heating it so much
it glowed in
X-ray light.
The panels on the left of the
above image show in X-rays that the
hot spots have moved out by more than three
light years in the time since the explosion,
with the left jet recently fading below detectability.
The drawing of the right depicts the
binary star system
that likely produced the X-ray jets,
with a normal red star on the left dumping matter into an
accretion disk around the
black hole on the right.
The jets are thought to be emitted along the
spin axis of the
black hole.
APOD: 2002 October 5 - X-Ray Cygnus A
Explanation:
Amazingly detailed,
this
false-color x-ray image is centered on the galaxy Cygnus A.
Recorded by the orbiting
Chandra Observatory, Cygnus A is
seen here as a
spectacular high energy x-ray source.
But it is actually more
famous at the low energy end of
the electromagnetic spectrum as one of
the brightest celestial radio sources.
Merely 700 million light-years distant,
Cygnus A is
the closest powerful radio galaxy and the false-color
radio image (inset right)
shows remarkable similarity to Chandra's x-ray view.
Central in both pictures, the center of
Cygnus A shines brightly while emission
extends 300,000 light-years to either side along the same axis.
Near light speed jets of atomic particles
produced by a massive central
black hole are believed to cause
the emission.
In fact, the x-ray image reveals "hot spots" suggestive
of the locations where the particle jets are stopped in
surrounding cooler, denser gas.
The x-ray image also shows that the jets have
cleared out a huge cavity in the surrounding gas.
Bright swaths of emission within the cavity likely indicate
x-ray hot material ... swirling toward the
central black hole.
APOD: 2002 September 28 - X-Ray Rainbows
Explanation:
A drop of water
or prism of
glass can spread out visible sunlight into
a
rainbow of colors.
In order of increasing energy, the well known spectrum of colors in
a rainbow
runs red, orange, yellow, green, blue, indigo, violet.
X-ray
light too can be spread out into
a spectrum
ordered by energy ... but not by drops of water or glass.
Instead, the orbiting
Chandra
X-ray Observatory
uses a set of 540 finely ruled, gold gratings to spread out the
x-rays, recording the results with digital detectors.
The resulting x-ray spectrum reveals much about the compositions,
temperatures, and motions within
cosmic x-ray sources.
This false color
Chandra image shows
the x-ray spectrum of a
star system in Ursa Major cataloged
as XTE J1118+480 and thought to consist of a sun-like star orbiting a
black hole.
Unlike the familiar appearance of a
prism's visible light rainbow,
the energies here are ordered
along radial lines with the highest energy x-rays near the center
and lowest energies near the upper left and lower right edges of the image.
The central spiky region itself is created by x-rays from the
source which are not spread out by the array of gratings.
APOD: 2002 September 20 - The Crab Nebula Pulsar Shrugs
Explanation:
How does a city-sized neutron star power the vast
Crab Nebula?
The expulsion of wisps of hot gas at high speeds appears
to be at least part of the answer.
Yesterday
time-lapse movies taken from both the
Chandra X-ray Observatory
and the
Hubble Space Telescope
were released showing a wisp of gas moving
out at about half the speed of light.
Wisps like this likely result from tremendous
electric voltages created by the central pulsar, a rapidly rotating,
magnetized, central
neutron star.
The hot plasma strikes existing gas, causing it glow in colors
across the
electromagnetic spectrum.
Pictured above is a composite image of the
center of the Crab Nebula
where red represents
radio emission, green represents
visible emission,
and blue represents
X-ray emission.
The dot at the very center is the hot
pulsar
spinning 30 times per second.
APOD: 2002 September 14 - X-Ray Moon
Explanation:
This x-ray image of the Moon
was made by the orbiting
ROSAT
(Röntgensatellit) Observatory in 1990.
In this digital picture, pixel brightness corresponds to x-ray intensity.
Consider the image in three parts:
the bright hemisphere of the x-ray moon,
the darker half of the moon,
and the x-ray sky background.
The bright lunar hemisphere shines
in x-rays because it scatters
x-rays emitted by the sun.
The background sky has an x-ray
glow in part due to
the myriad of distant, powerful active galaxies, unresolved
in the ROSAT picture but recently detected in Chandra Observatory
x-ray images.
But why isn't the dark half of the moon completely dark?
It's true that the dark lunar face is in
shadow and so is shielded
from direct solar x-rays.
Still, the few x-ray photons which seem to come from the moon's
dark half are currently thought to be caused by energetic particles in
the
solar wind bombarding the lunar surface.
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 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 August 20 - The Universe in Hot Gas
Explanation:
Where is most of the normal matter in the Universe?
Recent observations from the
Chandra X-ray Observatory confirm that it is in
hot gas filaments strewn throughout the universe.
"Normal matter" refers to
known elements and familiar fundamental particles.
Previously, the amount of
normal matter predicted by the
physics of the early universe exceeded the normal matter in
galaxies and
clusters of galaxies,
and so was observationally unaccounted for.
The Chandra observations found evidence for the massive and hot
intergalactic medium filaments by noting a slight dimming in
distant quasar
X-rays likely caused by hot
gas absorption.
The above image
derives from a computer simulation
showing an expected typical distribution of hot gas in a
huge slice of the universe
2.7 billion light-years across and 0.3 billion light years thick.
The distribution of much more abundant
dark matter likely mimics the normal matter,
although the composition of the
dark matter remains mysterious.
Both the distribution and the
nature of the even more abundant
dark energy also remain unknown.
APOD: 2002 August 12 - The Colors and Mysteries of Centaurus A
Explanation:
Why is spiral galaxy Centaurus A in so much turmoil?
The above composite image shows different clues to the
unusual galaxy's past in different bands of light.
In low energy radio waves, shown in red, lobes across the thick swath of
dust glow brightly.
In more energetic radio waves, depicted in green, a bright
jet is seen emanating from the
galaxy's center.
In optical light, shown in white, the stars that compose
much of the galaxy are visible.
Recently, Centaurus A
has recently been imaged in
X-ray light by the
Chandra X-ray Observatory.
The X-rays, depicted in blue, show arcs of hot gas
shooting out from the center in an explosion that
likely happened about 10 million years ago.
One hypothesis that would explain the turmoil would be if
Centaurus A
devoured a smaller galaxy
about 100 million years ago.
APOD: 2002 July 25 - NGC 1569: Heavy Elements from a Small Galaxy
Explanation:
For astronomers, elements other than
hydrogen and
helium
are sometimes considered to be simply "heavy elements".
It's understandable really, because even lumped all together
heavy elements make up an exceedingly small
fraction of the Universe.
Still, heavy elements can profoundly influence galaxy
and star formation ...
not to mention the formation of planets
and people.
In
this tantalizing
false-color x-ray image from the orbiting
Chandra
Observatory, small dwarf galaxy
NGC 1569 is
surrounded by
x-ray emitting
clouds of gas thousands of light-years
across.
The gas has
recently
been observed to contain significant
concentrations of astronomers' heavy elements such as oxygen, silicon,
and magnesium, supporting
the idea that dwarf galaxies,
the most common type of galaxy in the Universe,
are largely responsible for heavy elements
in intergalactic space.
A mere 7 million light-years distant toward the
long-necked
constellation
Camelopardalis,
NGC 1569 has undergone a recent burst of
star formation and stellar
supernova explosions.
The furious cosmic activity
has heated
the expanding gas clouds to temperatures of millions of degrees
while enriching them with newly synthesized
heavy elements.
APOD: 2002 July 11 - M51: X Rays from the Whirlpool
Explanation:
Fresh from yesterday's episode,
a popular pair of interacting galaxies
known as the
Whirlpool debut here beyond
the realm of visible
light -- imaged at high energies by the orbiting Chandra X-ray
Observatory.
Still turning in a remarkable performance, over 80 glittering
x-ray stars are present in
the
Chandra image data from the region.
The number of luminous x-ray
sources, likely neutron star and black hole
binary
systems within the confines of M51, is unusually high
for normal spiral or elliptical galaxies and suggests this cosmic
whirlpool has experienced
intense
bursts of massive star formation.
The bright cores of both galaxies, NGC 5194 and NGC 5195
(right and left respectively), also exhibit high-energy
activity in this false-color x-ray picture showing a diffuse
glow from multi-million degree gas.
An
expanded view of the region near the core of NGC 5194
reveals x-rays
from a supernova remnant, the debris from
a spectacular stellar explosion,
first detected by
earthbound astronomers in 1994.
APOD: 2002 June 17 - NGC 4697: X-Rays from an Elliptical Galaxy
Explanation:
The many bright, point-like sources in
this
Chandra Observatory x-ray image lie within NGC 4697, an
elliptical galaxy some 40 million
light-years away towards Virgo.
Like other normal
elliptical
galaxies, NGC 4697 is a spherical
ensemble of mainly older, fainter, low mass stars, with
little star forming gas and dust compared to spiral galaxies.
But the luminous x-ray
sources in the Chandra image indicate that
NGC 4697 had a wilder youth.
Powering the x-ray sources are neutron stars
and black holes in
binary
star systems, where x-rays are generated as matter from
a more ordinary companion star falls in to these bizarre,
compact objects.
Since neutron
stars and
black holes
are the endpoints in the lives of
massive stars, NGC 4697 must have had many bright, massive stars
in its past.
An exceptionally large number of NGC 4697's x-ray binaries are
found in the galaxy's globular star clusters, suggesting that
dense star clusters
are a good place for neutron stars and
black holes to capture a companion.
Stellar winds and
supernovae explosions of massive stars
could also have produced the hot gas responsible
for this galaxy's diffuse x-ray glow.
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 21 - The Galactic Center Radio Arc
Explanation:
What causes this unusual structure near the center of our Galaxy?
The long parallel rays slanting across the top of the
above radio image are known collectively as the
Galactic Center Radio Arc and jut straight out from the
Galactic plane.
The Radio Arc is connected to the
Galactic center
by strange curving filaments known as the Arches.
The bright radio structure at the bottom right
likely surrounds a
black hole at the
Galactic center and is known as
Sagittarius A*.
One origin hypothesis holds that the
Radio Arc and the Arches have their geometry
because they contain hot
plasma flowing along lines of constant
magnetic field.
Recent images from the
Chandra X-ray Observatory
appear to show this
plasma colliding with a nearby cloud of cold gas.
APOD: 2002 March 28 - Centaurus Galaxy Cluster in X-Rays
Explanation:
The Centaurus
Cluster is a swarm of hundreds of galaxies a
mere 170 million light-years away.
Like other immense
galaxy clusters, the Centaurus Cluster
is filled with gas at temperatures of 10 million degrees or more,
making the cluster a luminous source of
cosmic x-rays.
While individual galaxies are not seen here,
this
false-color x-ray image from the
Chandra
Observatory does reveal striking details of the
central region's hot cluster gas,
including a large twisted plume about 70,000 light-years long.
Colors represent temperatures indicated by the x-ray data with
red, yellow, green, and blue shades ranging in order from cool to hot.
The plume of gas alone is estimated to contain material equivalent
to about one billion times the mass of the Sun.
It may be a wake of gas condensing and
cooling along the path of
the massive, dominant
central galaxy moving through the cluster.
APOD: 2002 March 1 - Jupiter s Great X Ray Spot
Explanation:
The Solar System's largest planet,
gas
giant Jupiter, is famous
for its swirling
Great Red Spot.
In the right hand panel above, the familiar giant planet with
storm system and
cloud bands is shown in an
optical image from the passing
Cassini spacecraft.
In the left hand panel, a false-color image from the
orbiting
Chandra
Observatory presents a corresponding x-ray view of Jupiter.
The Chandra image
shows clearly, for the first time, x-ray spots and
auroral x-ray emission
from the poles.
The x-ray spot dominating the emission from Jupiter's
north pole (top)
is perhaps as surprising for astronomers today as the Great Red Spot
once
was.
Confounding previous theories,
the x-ray spot is too far north to be
associated with heavy electrically charged particles
from
the vicinity of volcanic moon Io.
Chandra data also show that the spot's
x-ray
emission mysteriously pulsates over a period of about 45 minutes.
APOD: 2002 February 8 - PKS 1127-145: Quasar View
Explanation:
The quasar known as
PKS 1127-145 lies
ten billion
light-years from our fair planet.
A Hubble Space Telescope
view in the left panel shows this quasar
along with other galaxies as they appear in optical light.
The
quasar itself is the brightest object in the lower right corner.
In the right panel is a
Chandra Observatory x-ray picture, exactly
corresponding to the Hubble field.
While the more ordinary galaxies are
not seen in the Chandra image,
a striking jet, nearly a million light-years long, emerges
from the quasar to dominate the x-ray view.
Bright in both optical and x-ray light, the quasar is thought to
harbor a supermassive black hole
which powers the jet and makes
PKS 1127-145
visible across the
spectrum -- a beacon from the
distant
cosmos.
APOD: 2002 January 16 - Abell 2597 s Cosmic Cavities
Explanation:
Typical of large galaxy clusters
billions of
light-years away,
Abell 2597 features hundreds of galaxies
embedded in a cloud
of multimillion degree gas which glows in x-rays.
This Chandra Observatory
x-ray
image shows the hot gas in this
cluster's central regions and also reveals two large dark cavities
within the x-ray glow; one below and right of center, the other
above and left.
Not a comment on dental health,
Abell 2597's cavities
are about 60,000 light-years across.
They are thought to be
remnants of a 100 million year old explosion originating
from a supermassive black hole at the cluster's core.
But the dim ghost
cavities are not completely
empty or they would have collapsed long ago.
Instead they are likely filled with hotter gas, high energy particles,
and magnetic fields and are moving away from the cluster center,
like bubbles rising in champagne.
Over the life of
a galaxy cluster such explosions may happen
over and over, creating a series of cavities which
transport
magnetic fields away from the cluster center.
In fact, radio observations
suggest another explosion has
since occurred in the center of Abell 2597.
APOD: 2002 January 10 - X-Ray Milky Way
Explanation:
If you had x-ray vision,
the center regions
of our Galaxy would not be hidden from
view by immense cosmic dust clouds
opaque to visible light.
Instead,
the Milky Way
toward Sagittarius might look something
like this stunning mosaic
of images from the orbiting
Chandra Observatory.
Pleasing to look at, the gorgeous false-color
representation of
the x-ray data shows
high energy x-rays in blue, medium energies in green,
and low energies in red.
Hundreds of white dwarf stars,
neutron stars, and black holes immersed in a
fog of multimillion-degree gas are included in the
x-ray vista.
Within the white patch at the image center lies
the Galaxy's central supermassive black hole.
Chandra's sharp
x-ray vision will likely lead to a new
appreciation of our Milky Way's most active neighborhood
and has already indicated that the hot gas itself may
have a temperature of a mere 10 million degrees Celsius
instead of 100 million degrees as previously thought.
The full mosaic is composed of 30 separate images and covers
a 900 by 400 light-year swath
at
the galactic center.
APOD: 2001 December 11 - Venusian Half Shell
Explanation:
Venus,
second planet from the Sun, appears above imaged for
the first time ever in x-rays (left) by the
orbiting Chandra Observatory.
Chandra's smoothed, false-color, x-ray
view is compared to
an optical image (right) from a small earthbound telescope.
Both show Venus illuminated by the Sun from the right, with
only half the sunward hemisphere visible, but at least one
striking difference is apparent.
While the optical image in
reflected sunlight is filled and
bright at the center, Venus in x-rays is bright around the edge.
Venus' x-rays are produced
by
fluorescence rather than reflection.
About 120 kilometers or so above the surface,
incoming solar x-rays
excite atoms in the Venusian atmosphere
to unstable energy levels.
As the atoms
rapidly decay back to their stable ground states they emit
a "fluorescence" x-ray, creating a glowing x-ray
half-shell above the sunlit hemisphere.
More x-ray emitting
material can be seen looking at the edge
of the shell, so the edge appears brighter in the x-ray image.
APOD: 2001 November 6 - In the Center of Spiral Galaxy M83
Explanation:
What's happening at the center of spiral galaxy M83?
Just about everything, from the looks of it.
M83, visible in the inset image on the upper left,
is one of the closest
spiral galaxies to our own
Milky Way Galaxy and from a distance of 15 million
light-years, appears to be relatively normal.
Zooming in on
M83's nucleus with the
latest telescopes, however, shows the center
to be an energetic and busy place.
Visible in the above image from the
Hubble Space Telescope
are bright,
newly formed stars and giant
lanes of dark
dust.
An
image with similar perspective from the
Chandra X-ray Observatory
shows the region is also rich in very hot gas and
small bright sources.
Observations with the large ground-based
VLT telescopes show the very
center likely has two separate nuclei.
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 October 24 - The Matter of Galaxy Clusters
Explanation:
Situated over 2,000,000,000 (two billion)
light-years from Earth, galaxies in cluster Abell 2390 (top) and
MS2137.3-2353 (bottom)
are seen in the right hand panels above,
false-color images from the
Hubble
Space Telescope.
Corresponding panels on the left reveal each cluster's
x-ray
appearance in images from the Chandra X-ray Observatory.
While the Hubble images record the cluster's star-filled galaxies,
the x-ray images show no galaxies at all ... only
multi-million degree hot intracluster gas
which glows in high energy x-rays.
But there lies a profound mystery.
The total mass in the galaxies on the right, plus the
mass of the hot gas on the left, falls far short of providing enough gravity
to confine the hot gas within
the galaxy clusters.
In fact,
the best accounting to date
can only find 13 per cent (!)
of the total matter necessary.
Gravitational lens
arcs visible in the deep Hubble images
also indicate these clusters have much more mass than directly identifiable
in the Chandra and Hubble data.
Astronomers conclude that most of the cluster matter is
dark matter,
invisible even to the combined far-seeing eyes of these orbiting
astrophysical observatories.
What is the
nature of this cosmic dark matter?
APOD: 2001 October 19 - X-Ray Stars and Winds in the Rosette Nebula
Explanation:
This mosaic of x-ray images
cuts a swath across the photogenic
Rosette Nebula, a stellar nursery 5,000 light-years from Earth
in the constellation Monoceros,
the
Unicorn.
Constructed from data recorded by the orbiting
Chandra X-ray Observatory,
the mosaic spans less than 100 light-years and is color
coded to show low energies in red and high energy x-rays in blue.
At the upper right is the young star cluster
NGC 2244, central to
the Rosette Nebula itself.
The hot outer layers of the massive stars are seen to be copious
sources of x-rays, but a diffuse x-ray glow
also pervades this cluster of newborn stars.
Since these stars are so young (less than few million years old!) the diffuse
x-ray emission is thought to be powered by energetic,
colliding
stellar winds rather
than remnants of supernovae explosions,
a final act in the
life cycle
of a massive star.
Moving away from the center, south and east across the nebula
(upper right to lower left),
the hot, blustery environment gives way to
dense molecular gas, absorbing low energy x-rays
while revealing the penetrating high energy x-rays from embedded stars.
APOD: 2001 September 20 - X Ray Stars in M15
Explanation:
Side by side, two
x-ray stars greeted astronomers in
this false-color Chandra Observatory
x-ray image of a
region near the core of globular star
cluster M15.
The greeting was a pleasant surprise, as all previous x-ray
images of the cluster showed only one such source where
Chandra's
sharper x-ray vision now reveals two.
These x-ray sources are modeled as
neutron star
binary systems.
Each is a city-sized neutron star in close orbit with
a normal stellar companion.
X-rays are generated
as matter from the normal star
falls onto
the compact neutron star.
This break through explains
why observations of the
previously recognized lone neutron star binary system in M15
were difficult to reconcile with any single model.
It also suggests that other globular star clusters which
roam the halo
of our Milky Way galaxy and
seem to contain
only one such neutron star x-ray source may in fact
contain more.
An optical Hubble Space Telescope image of the dense
M15 cluster is inset at the upper right.
APOD: 2001 September 19 - SIRTF: Name This Satellite
Explanation:
NASA is preparing to launch its next
Great Observatory in 2002, but it does not yet have a proper name.
Can you help?
Currently referred to only as the
Space Infrared Telescope Facility (SIRTF),
NASA
seeks to add something more significant.
Previously, NASA named its
Great Observatories for scientists of the recent past,
including the Hubble
Space Telescope, the
Compton
Gamma Ray Observatory and the
Chandra X-ray Observatory.
SIRTF will be the most powerful
infrared telescope ever launched,
imaging everything from nearby
planetary disks to
distant galaxies.
To enter the contest, one must
conform to all rules including the submission of an
essay of 250 words or less. The contest ends on December 20.
APOD: 2001 September 13 - X-Rays and the Circinus Pulsar
Explanation:
A bizarre
stellar
corpse 19,000 light-years from Earth,
pulsar
PSR B1509-58
beckons from the small southern constellation
of Circinus.
Like its cousin at the heart of the Crab nebula,
the Circinus pulsar is a rapidly spinning, magnetized
neutron star.
Seen in this false-color
Chandra Observatory
image, the environment
surrounding this cosmic powerhouse glows in high energy x-rays.
The Circinus
pulsar itself, thought to generate more than
7 quadrillion
volts (7 followed by 15 zeros), lies within the knot of bright
emission near the center of the picture.
Stretching toward the bottom left,
x-ray
emission traces a
jet of particles almost 20 light-years long
that seems to arise from the pulsar's south pole,
while the arc of bright emission
above the central knot is likely a shockwave produced by particles
driven from the pulsar's equator.
Near the top of the picture, lower energy x-ray emission shown in green
is from gas shock-heated to millions of degrees Celsius.
The shocked gas was produced by debris
blasted out from
the stellar explosion that
created the Circinus pulsar.
APOD: 2001 September 10 - Galactic Center Flicker Indicates Black Hole
Explanation:
Why would the center of our Galaxy flicker?
Many astronomers believe the only credible answer involves a
black hole.
During observations of
Sagittarius A* with the orbiting
Chandra X-ray Observatory, the bright
X-ray source at the very
center of our
Milky Way brightened dramatically for a few minutes.
Sagittarius A* is visible as the
bright dot near the center of the
above image.
Since large objects cannot vary quickly,
a small source is implicated in the variation.
Evidence including the
motions of central stars
indicates that the
center of our Galaxy
is a massive place, however, estimated to be over
a million times the mass of our
Sun.
Only one known type of object can fit
so much mass in so small a volume: a
black hole.
This short flicker therefore provides additional evidence that a
black hole does indeed reside at our
Galaxy's center.
If true,
the flicker might have been caused by an object
disrupting as it fell toward the
disruptive monster.
APOD: 2001 August 16 - Centaurus A: X-Rays from an Active Galaxy
Explanation:
Its core hidden
from optical view by a thick lane of dust, the giant elliptical
galaxy Centaurus A was among the first objects
observed by the orbiting Chandra X-ray Observatory.
Astronomers were not disappointed, as Centaurus A's
appearance in x-rays makes its classification as an
active galaxy easy to appreciate.
Perhaps the most striking feature of
this
Chandra false-color x-ray view
is the jet, 30,000 light-years long.
Blasting toward the upper left corner of the picture,
the jet
seems to arise from the galaxy's bright central x-ray source --
suspected of harboring a black hole with a million or so times
the mass of the Sun.
Centaurus A
is also seen to be teeming with other
individual x-ray sources and a pervasive, diffuse
x-ray glow.
Most of these individual sources are likely to be neutron stars
or solar mass black holes accreting material from their less
exotic binary companion stars.
The diffuse high-energy glow
represents gas throughout the galaxy
heated to temperatures of millions
of degrees C.
At 11 million light-years distant in the constellation
Centaurus,
Centaurus A (NGC 5128) is the closest
active galaxy.
APOD: 2001 August 14 - X-Rays from the Galactic Plane
Explanation:
In February 2000, the orbiting
Chandra X-ray Observatory spent 27 hours
staring into the plane
of our Milky Way galaxy.
Its target was a spot in the small
constellation
Scutum, within the Milky Way's
zone of avoidance where galactic
gas and dust clouds block visible light, making a poor
window for optical telescopes.
However the penetrating x-ray observations looked through
the obscurations revealing the Milky Way and the Universe beyond.
The x-ray view is
reconstructed above in false color.
Distant active galaxies
emitting high energy x-rays appear as blue dots,
while reddish dots are sources of lower energy x-rays,
likely stars within the
Milky Way itself.
Intriguing is the
diffuse blue glow of high energy x-rays,
distinct from the individual sources in the picture.
Astronomers have
long debated whether our galactic plane's apparently
extended x-ray emission
was due to discrete sources or diffuse hot gas.
As these results
suggest diffuse interstellar
gas with a temperature of tens of millions of degrees Celsius
is indeed the answer, other questions arise.
What heats the gas to these incredible temperatures?
Why does this energetic gas linger in the galactic plane?
APOD: 2001 July 25 - Hot Gas Halo Detected Around Galaxy NGC 4631
Explanation:
Is our Milky Way Galaxy
surrounded by a halo of hot gas?
A step toward solving this long-standing mystery
was taken recently with
Chandra X-ray observations of nearby galaxy
NGC 4631.
In the
above composite picture, newly resolved diffuse
X-ray emission is shown in blue, superposed on an
HST image
showing massive stars in red.
Since NGC 4631 is similar to the
Milky Way, this
observation indicates that our own Galaxy
is indeed surrounded by a halo of hot X-ray emitting gas,
although we are too close to clearly differentiate it from
more nearby extended X-ray sources.
The
clusters of massive stars
probably heat the halo gas.
Exactly how this gas gets ejected into a
halo is a topic of
continuing research.
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 June 7 - NGC 253: X-Ray Zoom
Explanation:
Astronomers now report
that Chandra X-ray Observatory
observations of galaxies known to be
frantically forming stars
show that these galaxies also
contain luminous x-ray sources -- thought to be
intermediate mass
black holes and immense clouds of superheated gas.
Take the lovely
island universe NGC 253 for example.
At distance of a mere 8 million light-years, NGC 253's prodigious
starforming activity has been well studied
using high-resolution optical images like the
one seen here at lower left.
Zooming in on this energetic galaxy's central region,
Chandra's
x-ray detectors reveal
hidden details indicated in the inset at right.
In the false-color image,
x-ray hot gas clouds glow near the core
and at least four very powerful x-ray sources
lie within 3,000 light-years of the center of the galaxy.
Much more luminous than
black hole binary star systems in our own
galaxy, these extreme x-ray sources may be gravitating toward
NGC 253's center.
As a result,
NGC 253 and other similar starforming galaxies
could ultimately develop a single, central, supermassive black hole,
transforming their cores into quasars.
APOD: 2001 May 24 - X-Ray Stars of 47 Tucanae
Explanation:
A deep optical image (left)
of 47 Tucanae shows an ancient
globular star cluster so dense and crowded that individual stars
can not be distinguished in its closely packed core.
An
x-ray image of its central regions (inset right) from the
Chandra
Observatory reveals a wealth of x-ray stars hidden there.
Color-coded by energy, low energies are red, medium are green,
and high energy cosmic
x-ray sources are blue, while
whitish sources are bright across the x-ray energy bands.
The x-ray stars here are double stars or "compact"
binary star systems.
They are so called because one of the pair of stellar companions is
a normal star and the other a compact object --
a white dwarf,
neutron star,
or possibly a black hole.
Chandra's
x-ray vision detects the presence of
an unexpectedly large number of these exotic star systems
within 47 Tucanae, but it also indicates the apparent
absence of a large central black hole.
The finding suggests that compact binary star systems of
47 Tucanae
may be ejected from the cluster before coalescing
to form a large black hole at its core.
APOD: 2001 May 16 - The Center of the Circinus Galaxy in X-Rays
Explanation:
Are black holes the cause of X-rays that pour out
from the center of the
Circinus galaxy?
A new high-resolution image from the orbiting
Chandra X-ray Observatory has resolved the
inner regions of this nearby galaxy into
several smaller sources.
The image is shown above in representative-color.
Extended
X-ray emission from the center appears to
match optical light and appears consistent
with a model where hot gas is escaping from a
supermassive black hole at
Circinus' center.
At least one of the other sources varies
its X-ray brightness as expected from a
binary star system,
indicating that the system is small yet massive,
and giving credence to a model where a
black hole
is surrounded by doughnut-shaped ring.
The region shown spans about 5000
light-years across.
APOD: 2001 May 11 - X-Ray Rainbows
Explanation:
A drop of water
or prism of
glass can spread out visible sunlight into
a
rainbow of colors.
In order of increasing energy, the well known spectrum of colors in
a rainbow
runs red, orange, yellow, green, blue, indigo, violet.
X-ray
light too can be spread out into
a spectrum
ordered by energy ... but not by drops of water or glass.
Instead, the orbiting
Chandra
X-ray Observatory
uses a set of 540 finely ruled, gold gratings to spread out the
x-rays, recording the results with digital detectors.
The resulting x-ray spectrum reveals much about the compositions,
temperatures, and motions within
cosmic x-ray sources.
This false color
Chandra image shows
the x-ray spectrum of a
star system in Ursa Major cataloged
as XTE J1118+480 and thought to consist of a sun-like star orbiting a
black hole.
Unlike the familiar appearance of a
prism's visible light rainbow,
the energies here are ordered
along radial lines with the highest energy x-rays near the center
and lowest energies near the upper left and lower right edges of the image.
The central spiky region itself is created by x-rays from the
source which are not spread out by the array of gratings.
APOD: 2001 April 13 - GRB010222: Gamma Ray Burst, X Ray Afterglow
Explanation:
A
fading afterglow from one of the most powerful explosions
in the universe is centered in this
false
color image from the spacebased
Chandra X-ray Observatory.
The cosmic explosion, an enormously bright
gamma-ray
burst (GRB), originated in a galaxy billions
of light-years away and was detected by the
BeppoSAX
satellite on February 22.
GRB010222
was visible for only a few seconds at
gamma-ray energies, but its afterglow
was
followed for days by x-ray, optical, infrared and radio instruments.
These Chandra observations of the GRB's
x-ray glow hours after
the initial explosion suggest an expanding fireball of material
moving at near light speed has hit a wall of relatively dense gas.
While the true nature of gamma-ray bursters remains unknown,
the mounting evidence from
GRB afterglows does indicate that
the cosmic blasts may be hypernovae -- the
death explosions of very massive, short-lived stars
embedded in active star forming regions.
As the hypernova
blasts sweep up dense clouds of material in the
crowded star forming regions they may also trigger more
star formation.
APOD: 2001 March 28 - Chandra Deep Field
Explanation:
Officially the
Chandra
Deep Field - South, this picture represents the deepest ever
x-ray image of the Universe.
One million seconds of accumulated exposure time with the orbiting
Chandra X-ray Observatory went in to its making.
Concentrating on a single, otherwise unremarkable patch
of sky in the constellation
Fornax,
this x-ray image corresponds to the
visible light Hubble Deep Field - South
released in 1998.
Chandra's view, color coded with low energies in red, medium in green,
and high-energy x-rays in blue, shows many faint sources of relatively
high-energy x-rays.
These are likely active galaxies feeding supermassive central
black holes
and large clusters of galaxies
at distances of up to 12 billion light-years.
The stunning picture supports
astronomers' ideas
of a youthful
universe
in which massive black holes were much more dominant
than at present.
APOD: 2001 March 9 - X-rays From HCG 62
Explanation:
Scanning the skies for galaxies Canadian astronomer
Paul Hickson and colleagues identified some 100 compact
groups
of galaxies, now appropriately called
Hickson Compact Groups (HCGs).
With only a few member galaxies per group, HCGs are much smaller
than the immense
clusters of galaxies
which lurk in the cosmos,
but like the large galaxy clusters, some HCGs seem to be filled with
hot,
x-ray emitting gas.
In fact, groups of galaxies like HCGs may
be the building blocks of the large clusters.
This false-color x-ray image from the orbiting
Chandra
Observatory reveals x-ray emission from the gas in
one
such group, HCG 62, in startling detail.
In the image, black and green colors
represent low intensities while red and purple hues indicate
high x-ray intensities.
Striking features of the
x-ray image are the low brightness blobs
at the upper left and lower right
which symmetrically flank the intense central x-ray region.
HCG 62 lies in Virgo,
and near the group's center resides elliptical
galaxy
NGC 4761.
At optical wavelengths,
some HCGs
make for
rewarding viewing,
even with modest sized telescopes.
APOD: 2001 February 22 - 3C294: Distant X Ray Galaxy Cluster
Explanation:
Large
clusters of galaxies
are the most massive objects in the universe.
Astronomers now realize that a hallmark of these cosmic behemoths
are gas clouds with temperatures of tens of millions of
degrees that
pervade the clusters and radiate
strongly in x-rays.
This
Chandra Observatory image
centered on a
radio galaxy cataloged as
3C294 indeed reveals the telltale
hot x-ray gas in an hourglass shaped
region surrounding the dominant galaxy and
shows the presence of a massive galaxy cluster in the
distant universe.
Here the picture is color-coded by x-ray energy, red for low, green
for medium, and blue for high energy x-rays.
The cluster associated with 3C294
is 10 billion light-years away making it the
most distant x-ray galaxy cluster
ever detected.
Objects at that extreme distance existed when the universe was
young, a mere 20 percent of its present age.
Impressively, this observation demonstrates that even at those early
times massive
clusters of galaxies were already present.
APOD: 2001 January 24 - NGC 3603: X-Rays From A Starburst Cluster
Explanation:
A mere 20,000 light-years from
the Sun lies the
NGC 3603 star cluster,
a resident of the nearby
Carina
spiral arm
of our Milky
Way galaxy.
Seen here in this recent false-color
x-ray image from the Chandra Observatory,
NGC 3603
is well known to astronomers
as a young cluster in a large
galactic star-forming region.
The image colors were chosen to show the relative x-ray brightness
of the many individual sources present, where
green are faint and red to purple hues are bright sources of x-rays.
The stars in the cluster were formed in a single "burst" of star
formation only one or two million years ago,
so the x-rays are believed to come from the massive young
stars themselves or from their energetic stellar winds.
Since other common galactic
sources
of x-rays such as
supernova remnants and neutron stars
represent final stages in the life of a massive
star, they are unlikely to be present in such a young cluster.
Nearby NGC 3603 is thought to be a convenient
example of the star clusters that populate
distant starburst galaxies.
APOD: 2001 January 19 - Black Holes Are Black
Explanation:
Q: Why are
black holes black?
A: Because they have an
event horizon.
The event horizon is that one-way boundary predicted by
general
relativity beyond which nothing, not even light, can return.
X-ray
astronomers using the space-based Chandra Observatory now
believe they have direct evidence for event horizons - therefore
black holes - in binary star systems which can be
detected in x-ray light.
These binaries, sometimes called x-ray novae, are
known to consist of relatively normal stars dumping
material on to massive, compact companions.
As illustrated,
the material swirls toward the companion in an
accretion disk which itself glows in x-rays.
If the compact companion is a neutron star
(right), the material ultimately smashes into the solid surface
and glows even more brightly in high energy x-rays.
But if it is indeed a
black hole with a defining event
horizon, then the x-ray hot material approaches the speed of
light as it swirls past the surface of no
return and is lost from view.
Recent
work describes observations of two classes of
x-ray binaries,
one class 100 times fainter than the other.
The results imply the presence of an event horizon in the
fainter class which causes the extreme difference in x-ray
brightness.
APOD: 2001 January 11 - X-rays From The Cat's Eye
Explanation:
Haunting patterns within planetary nebula
NGC 6543
readily suggest its popular moniker -- the Cat's Eye nebula.
In 1995, a stunning false-color optical image
from the Hubble
Space Telescope detailed the swirls of this
glowing nebula, known to
be the gaseous shroud expelled from a dying
sun-like
star about 3,000 light-years from Earth.
This composite picture combines the famous Hubble image
with new x-ray data from the
orbiting
Chandra Observatory and reveals
surprisingly intense x-ray emission indicating the presence
of extremely hot gas.
X-ray emission is shown as blue-purple hues superimposed on red and
green optical emission.
The nebula's central star itself is clearly immersed in
the multimillion degree, x-ray emitting gas.
Other pockets of x-ray hot gas seem to be bordered by cooler
gas emitting strongly at optical wavelengths, a clear indication
that expanding hot gas is sculpting the
visible Cat's Eye
filaments and structures.
Gazing into the Cat's Eye, astronomers see
the fate of our sun,
destined to enter its own
planetary nebula phase
of evolution ... in about
5 billion
years.
APOD: 2000 December 30 - A Year of Resolving Backgrounds
Explanation:
No matter which direction you look,
no matter what type of light you see,
the sky glows - but why?
The sources of many of these
background radiations have remained long-standing puzzles,
but this millennial year brought some partial resolutions.
In X-ray light the recently launched spacecraft
Chandra and
XMM
resolved much of the seemingly uniform
X-ray background into many discrete sources, many of which appear to be
black holes at the centers of galaxies
accreting matter.
In
microwave light, the
BOOMERANG and
MAXIMA-1 missions
resolved with
new clarity
the seemingly uniform
microwave background.
The size and distribution of these
spots indicates a
geometrically flat universe,
which, when combined recent
supernovae results,
indicate a universe with an accelerating expansion rate
filled with
dark matter and
dark energy.
Pictured above, a map spanning ten degrees of the
microwave sky resolves the
microwave background
into hot and cold spots, as indicated in microkelvins.
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 8 - Abell 1795: A Galaxy Cluster s Cooling Flow
Explanation:
Throughout the Universe, galaxies
tend to swarm in groups
ranging from just a handful of members to casts of thousands.
Astronomers have realized since the early 1970s that
the larger swarms, immense
clusters of galaxies millions of
light-years across, are immersed
within tenuous clouds of hot gas which glow strongly in x-rays.
These clouds may have been heated by their collapse
in the early Universe, but in many
galaxy clusters,
the gas appears to be cooling.
This Chandra Observatory
x-ray image reveals a striking
cooling flow
in the central regions of the
galaxy
cluster
cataloged
as Abell 1795.
Brighter pixels in the false-color image represent higher x-ray
intensities.
The bright filament down the center indicates gas condensing and
cooling -- rapidly
loosing energy by radiating x-rays.
At the very top of the filament is a
large, x-ray bright galaxy.
As it moved through the
cluster gas cloud, the massive galaxy's gravitational
influence seems to have created this cosmic wake of denser,
cooling gas.
Continuing to cool, the cluster gas will ultimately
provide raw material to form future generations of stars.
APOD: 2000 November 10 - X-Ray Cygnus A
Explanation:
Amazingly detailed,
this
false-color x-ray image is centered on the galaxy Cygnus A.
Recorded by the orbiting
Chandra Observatory, Cygnus A is
seen here as a
spectacular high energy x-ray source.
But it is actually more
famous at the low energy end of
the electromagnetic spectrum as one of
the brightest celestial radio sources.
Merely 700 million light-years distant,
Cygnus A is
the closest powerful radio galaxy and the false-color
radio image (inset right)
shows remarkable similarity to Chandra's x-ray view.
Central in both pictures, the center of
Cygnus A shines brightly while emission
extends 300,000 light-years to either side along the same axis.
Near light speed jets of atomic particles
produced by a massive central
black hole are believed to cause
the emission.
In fact, the x-ray image reveals "hot spots" suggestive
of the locations where the particle jets are stopped in
surrounding cooler, denser gas.
The x-ray image also shows that the jets have
cleared out a huge cavity in the surrounding gas.
Bright swaths of emission within the cavity likely indicate
x-ray hot material ... swirling toward the
central black hole.
APOD: 2000 October 31 - The Perseus Cluster s X Ray Skull
Explanation:
This haunting image from the orbiting
Chandra Observatory
reveals the Perseus Cluster of Galaxies
in x-rays,
photons with a thousand or more times the energy of visible light.
Three hundred twenty million light-years distant, the
Perseus Cluster
contains thousands of galaxies, but none of them are
seen here.
Instead of mere galaxies, a fifty million degree cloud of
intracluster gas, itself more
massive than all the cluster's galaxies
combined, dominates the x-ray view.
From this angle, voids and bright knots in the
x-ray hot gas cloud lend it a very
suggestive appearance.
Like eyes in a skull, two dark bubbles flank a bright central source
of x-ray emission.
A third elongated bubble (at about 5 o'clock) forms a toothless mouth.
The bright x-ray source is likely a supermassive black hole at the
cluster center with the bubbles blown by explosions of
energetic particles ejected from the black hole and expanding into
the immense gas cloud.
Fittingly, the dark spot forming the skull's "nose" is an
x-ray shadow ... the shadow of a large galaxy inexorably falling into
the cluster center.
Over a hundred thousand light-years across, the Perseus Cluster's
x-ray skull is a bit larger than skulls you
may see tonight.
Have a safe and happy Halloween!
APOD: 2000 October 6 - X-Rays From Sirius B
Explanation:
In visible light
Sirius A
(Alpha Canis Majoris) is the
brightest
star in the night sky, a closely watched celestial beacon throughout
recorded
history.
Part of a
binary star system only 8 light-years away,
it was known in modern times to have a small
companion star,
Sirius B.
Sirius B is much dimmer and
appears so close to the brilliant Sirius A
that it was not
actually
sighted until 1862,
during Alvan Clark's testing
of a large, well made optical
refracting telescope.
For orbiting x-ray telescopes, the
Sirius situation is exactly
reversed, though.
A smaller but hotter Sirius B appears as the overwhelmingly
intense x-ray source in this Chandra Observatory
x-ray
image (lines radiating from Sirius B are image artifacts).
The fainter source seen at the position of Sirius A
may be largely due to ultraviolet light from the star leaking
into the x-ray detector.
With a surface temperature of 25,000
kelvins,
the mass of the Sun, and a radius just less than Earth's, Sirius B
is the closest known
white dwarf star.
Can you guess what makes
Sirius B like
Neptune,
the Sun's most distant gas giant planet?
While still unseen, the presence of both celestial
bodies was detected based on their gravitational
influence alone ... making them early examples of
dark
matter.
APOD: 2000 September 14 - M82 s Middle Mass Black Hole
Explanation:
Black
holes are probably the most
bizarre
creatures in
the modern astronomical zoo.
And after years of pondering
black
holes as either stellar mass objects seen in
binary star systems or enormous
supermassive black holes at the
centers of galaxies,
astronomers now have strong evidence for another exotic species --
middle mass black holes.
The leading candidate for the ultradense middle ground is
indicated in this false-color detail of a sharp x-ray picture
from the space-based Chandra Observatory.
A close-up of x-ray sources near the center of
starburst galaxy M82,
the cropped
Chandra
image spans about 4,000 light-years.
M82 itself is around 11 million light-years distant.
The arrowed source has recently been convincingly demonstrated to
exhibit x-ray characteristics of an object whose
gravitational field holds more than 500 times the mass of the sun
within a volume the size of the moon!
Astronomers
also
note that unlike the supermassive variety
which are thought to lie at the centers of galaxies, this
middle mass black hole is about 600 light-years from the
center of M82.
Theories for the formation of a middle mass black hole
include the collapse of a "hyperstar"
formed by
the coalescence of many normal stars, or the
direct
merger of stellar mass black holes.
APOD: 2000 September 2 - X Ray Moon
Explanation:
This x-ray image of the Moon
was made by the orbiting
ROSAT
(Röntgensatellit) Observatory in 1990.
In this digital picture, pixel brightness corresponds to x-ray intensity.
Consider the image in three parts:
the bright hemisphere of the x-ray moon,
the darker half of the moon,
and the x-ray sky background.
The bright lunar hemisphere shines
in x-rays because it reflects
x-rays emitted by the sun ... just as it shines
at night by reflecting visible sunlight.
The background sky has an x-ray
glow in part due to
the myriad of distant, powerful active galaxies, unresolved
in the ROSAT picture but recently detected in Chandra Observatory
x-ray images.
But why isn't the dark half of the moon completely dark?
It's true that the dark lunar face is in
shadow and so is not
reflecting solar x-rays.
Still, the few x-ray photons which seem to come from the moon's
dark half are currently thought to be caused by energetic particles in
the
solar wind bombarding the lunar surface.
APOD: 2000 August 18 - X-Rays From Antennae Galaxies
Explanation:
A bevy of
black
holes and
neutron stars
shine as bright, point-like
sources against bubbles of
million degree gas in this
false-color x-ray image from the
orbiting Chandra Observatory.
The striking picture shows the central regions of two
galaxies, NGC 4038 and NGC 4039, locked in a titanic collision
some 60 million light-years distant in the
constellation Corvus.
In visible
light images, long, luminous, tendril-like structures emanating
from the wreckage lend the pair their
popular moniker, the Antennae Galaxies.
Galactic collisions are now thought to be fairly common, but when
they happen individual stars rarely collide.
Instead gas and dust clouds merge and compress, triggering furious
bursts of massive
star
formation with thousands of resulting supernovae.
The exploding stars litter the scene with
bubbles
of shocked hot gas and
collapsed stellar cores.
Transfixed by this cosmic accident
astronomers watch and are beginning
to
appreciate the collision-driven evolution
of galaxies, not unlike
our own.
APOD: 2000 August 1 - X-Rays from Comet LINEAR
Explanation:
Why do comets emit X-rays?
First discovered
during the passing of
Comet Hyakutake in 1996,
the reason a cold
comet
would produce hot
X-rays has since remained a mystery.
On July 14, however, the orbiting
Chandra X-ray Observatory was able to
provide an image of passing
Comet LINEAR,
shown above, in enough detail to unravel the mystery.
The key to the
solution turns out to be the unusual
wind of fast ions emitted by our
Sun.
These
ions apparently collide with gas recently emitted by the
comet and cause some ions to
acquire a new
electron.
An
electron
that starts in a high-energy state will emit an
X-ray as it falls in closer to the ion
nucleus.
As other comets move into the inner Solar System, this discovery should allow
future study of the continually evolving gas cloud that surrounds
comets as well as the composition of the
solar wind.
APOD: 2000 July 13 - LP 944-20: A Failed Star Flares
Explanation:
The tiny spot circled on the right actually represents a big
astronomical discovery -- the first detected
flare from a failed star.
Failed stars, termed
brown dwarfs in astronomers'
parlance,
are too low in mass to ignite nuclear hydrogen burning in their cores,
yet still shine feebly as the energy from
their gravitational collapse is converted to heat and light.
In fact, the
dim brown dwarf cataloged as LP944-20 is
estimated to have only
6 percent the mass of the Sun (60 times the mass of Jupiter) and
one-tenth the Sun's diameter.
A mere 16 light-years distant in the southern constellation Fornax
it is well studied,
but this failed star recently
startled astronomers
by producing a
flare visible at
x-ray energies.
The above
Chandra X-ray Observatory
images of the LP944-20 star field were
recorded in December 1999.
Showing nothing (left) for the first
nine hours, the brown dwarf generated a significant x-ray flare during the
final hours of the observation.
How did a failed star produced such a
high-energy flare?
Magnetic fields twisted and broken by turbulent motions near the surface
of the brown dwarf may be the culprit.
Difficult to detect
because they are otherwise faint, brown dwarf stars
are believed to be common throughout the galaxy.
APOD: 2000 June 19 - The Long Jet of Pictor A
Explanation:
A jet stretching nearly a million light years
has been imaged emanating from galaxy Pictor A.
The thin
jet of
electrons and
protons
shoots out at
nearly light-speed
likely from the vicinity of a large
black hole at the galaxy center.
At the left of the
above image in
X-rays is the radio galaxy
Pictor A, known as a
radio galaxy for its strong
radio emission.
At the far end of the
jet on the right a
hot spot glows as the intense particle beam bores
through a gas cloud in intergalactic space.
The jet and hot spot of
Pictor A had been seen previously in radio waves,
but only recently has the orbiting
Chandra X-ray Observatory confirmed its unusual power.
APOD: 2000 June 15 - X-Rays From The Perseus Cluster Core
Explanation:
The Perseus Cluster
of thousands of galaxies, 320 million
light-years distant, is
one of
the most massive objects
in
the Universe.
At its core lies the giant cannibal galaxy
Perseus A
(NGC 1275), accreting matter as
gas and galaxies fall into it.
Representing low, medium, and high energy
x-rays as red, green,
and blue colours respectively,
this Chandra X-ray Observatory image
shows remarkable details of x-ray emission from this monster galaxy and
surrounding hot (30-70 million degrees C)
cluster gas.
The bright central source is the supermassive
black
hole at the core of Perseus A itself.
Dark circular voids just above and below the galaxy center,
each about half the size of our own
Milky Way Galaxy,
are believed to be magnetic bubbles of
energetic particles
blown by the accreting black hole.
Settling
toward
Perseus A, the cluster's x-ray hot gas piles up
forming bright regions around the bubble rims.
Dramatically, the long greenish wisp just above the galaxy's centre
is likely the x-ray shadow produced by
a small galaxy falling into the burgeoning
Perseus A.
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 June 1 - X-Ray Wind From NGC 3783
Explanation:
A black
hole is supposed to inexorably attract matter.
But the intense radiation generated as material swirls and plunges into
its high gravity field also heats up surrounding gas and drives it away.
In fact, measurements made using
this recent Chandra Observatory X-ray
spectrum of active galaxy
NGC 3783
reveal a wind of highly ionized
atoms blowing away from the galaxy's suspected
central
black hole at a million miles per hour.
Displayed in false color, the bright central spot is the
X-ray image of NGC 3783 while the
lines radiating away represent
an X-ray
spectrum of this source
produced by Chandra's
High
Energy Transmission Grating (HETG).
An X-ray spectrum is the analog to
the rainbow spread of colors in a visible light spectrum.
It represents a detailed, spread out image of X-ray colors or
energies arising from the source.
Ionized atoms of iron, magnesium, oxygen, nitrogen and other
elements produce
patterns of absorption at known X-ray energies.
These patterns have been identified in
the spectrum of NGC 3783 at slightly shifted energies
and the measured shifts indicate the hot wind's velocity.
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 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 March 6 - Abell 2142: Clash of the Galaxy Clusters
Explanation:
Over the course of billions of years,
whole clusters of galaxies merge.
Above is an
X-ray image of
Abell 2142, the result of the collision of two huge
clusters of galaxies,
and one of the most massive objects known in the universe.
This false-color image shows a
concentration of gas 50 million
degrees hot near the center of the resulting cluster.
Oddly, it is the relative coldness of the gas that makes
this situation particularly interesting.
The center of Abell 2142 is surrounded by gas fully twice as hot,
a temperature thought to have been created by
energy released during the
colossal collision.
Still, since we can only see a snapshot in time,
much remains unknown about how
clusters of galaxies
form and coalesce.
APOD: 2000 February 4 - X-Ray Stars Of Orion
Explanation:
The stars of Orion shine brightly
in northern winter skies where
the constellation
harbors the closest large stellar nursery,
the Great Nebula of Orion, a mere 1500 light-years away.
In fact, the apparently bright clump of stars near the center
of this Chandra
X-ray telescope picture of a portion of
the nebula are the massive stars of
the Trapezium - the
young star cluster which powers much of the nebula's
visible-light glow.
But the sheer number of other stars seen in
this X-ray image, which
spans about 10 light-years, has surprised and delighted astronomers
and
this picture was recently touted
as the richest field of X-ray sources ever recorded
in a single observation.
The picture does dramatically illustrate that
young stars are prodigious sources
of X-rays,
thought to be produced in hot
stellar coronas and
surface flares in a young star's strong magnetic field.
Our middle-aged Sun
itself was probably thousands of times
brighter in X-rays when, like
the Trapezium stars, it was
only a few million years old.
The dark lines through the image are instrumental artifacts.
APOD: 2000 January 21 - X For Andromeda
Explanation:
A big beautiful spiral galaxy 2 million light-years away,
Andromeda (M31)
has long been touted as an analog to the Milky Way,
a distant mirror of our own galaxy.
The popular 1960s British sci-fi series,
A For Andromeda,
even postulated that it was home to another technological civilization
that communicated
with us.
Using the newly unleashed observing power of the orbiting
Chandra X-ray telescope,
astronomers have now imaged the
center of our near-twin
island universe, finding evidence
for an object so bizarre it would have impressed many
60s science fiction writers (and readers).
Like the Milky Way,
Andromeda's galactic center appears to
harbor an X-ray source characteristic of
a black hole of a million or more solar masses.
Seen above,
the false-color X-ray picture shows a number of
X-ray sources, likely
X-ray binary stars, within
Andromeda's central region as yellowish dots.
The blue source located right at the galaxy's center is coincident
with the position of the suspected massive black hole.
While
the X-rays are produced as material falls into the
black hole and heats up, estimates from the X-ray data show Andromeda's
central source to be surprisingly cool - only a million
degrees or so compared to the tens of millions of degrees
indicated for Andromeda's X-ray binaries.
APOD: 2000 January 20 - X-Rays From The Galactic Center
Explanation:
Exploring quasars
and active galaxies in the distant
universe, astronomers have come to believe that
most galaxies have massive black holes at their centers.
Swirling stars and a strong, variable
radio source offer convincing evidence that even our own Milky Way
galaxy's center harbors such a
bizarre object,
a mere 30,000 light-years away.
Still, it has long been realized that if a massive black hole
lurks there
it should produce X-rays
- which have not previously been identified.
Now, though relatively faint,
the missing X-ray source may have been found.
Taking advantage of the sensitive Chandra Observatory
astronomers have recorded this false-color
X-ray image of the Galactic Center.
Embedded in a diffuse cloud of
X-ray hot gas,
the white dot at the center corresponds to an X-ray
source at exactly the position of the strong radio source
and suspected black hole.
Other individual X-ray sources are also present in
the picture which spans about 10 light-years at the distance
of the galactic center.
With radio and X-ray emission generated by infalling material,
the Milky Way's central black hole is thought to have a mass of
over 2 million suns.
APOD: 2000 January 14 - Chandra Resolves the Hard X Ray Background
Explanation:
It is everywhere but nobody knew why.
In every direction at all times, the
sky glows in
X-rays.
The
X-ray background phenomenon was discovered over 35 years ago,
soon after the first
X-ray satellites were launched,
and has since gone unexplained.
Yesterday
results were released using data from the recently launched
Chandra X-Ray Observatory
that appears to have resolved much of this mystery.
The above photograph shows that about 80 percent of the apparently diffuse
hard X-ray background
can be resolved into very many very faint sources.
The new question is now what are these sources?
Early speculation, much of which
predates these observations, holds that many of these sources are the
active centers of
distant galaxies,
probably involving
massive black holes.
Still other sources may be of origins currently unknown.
APOD: December 28, 1999 - A Year of New Perspectives
Explanation:
Fittingly, 1999 saw a decade of astronomical
discoveries
to an end with portents of things to come - embodied in
new spacecraft, telescopes, and perspectives to explore the
distant Universe across the electromagnetic spectrum.
X-ray astronomy in particular will likely flourish in coming years,
judging from this year's successful launch of the
triple-barrelled
X-ray Multi-Mirror satellite and
spectacular first results from the orbiting
Chandra X-ray Observatory.
Ground-based astronomy will flourished too as
very large telescopes and
new instruments have come
online or near completion.
Radio astronomers also achieved an observational
milestone this year with the
record breaking VLBI observations
from a network of radio telescopes
as large as planet Earth.
But the APOD editors' favorite astronomical screensaver
of 1999 has leveraged
the phenomenonal growth of the internet and the
personal computer boom to support the Search
for ExtraTerrestrial Intelligence in
the SETI@home project -
which has now likely involved more computer power than any
other project in history.
APOD: December 21, 1999 - XMM Launched
Explanation:
X-ray astronomy entered a golden age
earlier this month with the successful launch of the
X-ray Multi-Mirror
(XMM) satellite.
XMM's three huge telescope barrels each hold
58 concentric cylindrical mirrors,
together totaling a surface area rivaling a
tennis court.
Each mirror has been
gold plated to less than one-millimeter thickness to
reflect normally penetrating
X-rays.
ESA's XMM joins
NASA's Chandra X-ray Observatory
as leading observatories in X-ray astronomy.
The
XMM satellite also carries a small optical and
ultraviolet telescope.
XMM's unusually elliptical orbit around the Earth peaks nearly one-third
of the way to the Moon.
XMM's observing program during its planned two-year
mission includes monitoring the hot surroundings of
black holes,
the fiery regions surrounding the
centers of galaxies,
the mysterious
X-ray background
light that appears to come from all directions, and the
hot gas that glows between galaxies and stars.
APOD: December 17, 1999 - Hot Gas In Hydra A
Explanation:
The Hydra A galaxy cluster is really big.
In fact, such
clusters of galaxies
are the largest gravitationally
bound objects in the Universe.
But
individual galaxies are too cool to be recorded
in this false-color
Chandra Observatory X-ray image which
shows only the 40 million degree gas
that permeates the Hydra A cluster.
Astronomers have discovered that such
X-ray hot gas clouds,
millions of light-years across, are common
in galaxy clusters.
They
expected the gas
to be cooling and smoothly flowing into the clusters' central regions
to form new galaxies and stars.
Instead, the Chandra image shows
details around the X-ray bright cluster core
which suggest that magnetic fields and explosive
events disturb the flow, deflecting the gas
into loops and long structures and possibly inhibiting the
formation of more cluster galaxies and stars.
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 25, 1999 - 3C 295: X-rays From A Giant Galaxy
Explanation:
Did this galaxy eat too much?
Five billion light-years away,
the giant elliptical galaxy 3C295
is a prodigious source of
energy at radio wavelengths.
Bright knots of
X-ray emission are also seen at the center of
this false-color Chandra Observatory image of the region.
The X-ray and radio emission are believed to be the result of
an explosive event triggered when too much material flowed
into a supermassive
black hole at the heart of the giant galaxy.
Additionally, the
Chandra
picture beautifully reveals an extensive
cloud of 50 million degree gas surrounding
3C295.
Embedded in the cloud is a
cluster of about 100 galaxies,
too cool to be seen in the X-ray picture.
About two million light-years across, the
X-ray hot cloud
itself contains enough material to create another
1,000 galaxies or so making the cluster and cloud among
the most massive objects in the Universe.
However, X-ray data indicate that there is
still not enough observed mass to hold the cloud and cluster together
gravitationally,
suggesting the presence of large amounts of
dark matter.
APOD: October 28, 1999 - X Ray Jet From Centaurus A
Explanation:
Spanning over 25,000 light-years, comparable to the distance from
the Sun to the center of our own Milky Way galaxy, a
cosmic jet seen in X-rays blasts from
the center of Centaurus A.
Only 10 million light-years away,
Centaurus A is a giant
elliptical galaxy - the closest
active galaxy to Earth.
This composite image illustrates
the jumble of gas, dust, and stars visible
in an optical picture
of Cen A superposed on
a new image recorded by the orbiting
Chandra X-ray Observatory.
The X-ray data is shown in red.
Present theories hold that the X-ray bright jet
is caused by electrons driven to extremely high energies
over enormous distances.
The jet's
power source is likely to be a black hole with about 10 million
times the mass of the Sun
coincident with the X-ray bright spot at the galaxy's center.
Amazingly, while
some material in the vicinity of the black hole
falls in, some material is blasted outward in energetic jets.
Details of this
cosmic power
generator can be explored with the
Chandra X-ray data.
APOD: October 11, 1999 - Eta Carinae in X Rays
Explanation:
Eta Carinae is the one of the most luminous star systems in
our Galaxy,
radiating millions of times more power than
our Sun.
Eta Carinae is also
one of the strangest star systems known,
brightening and fading greatly since the early 1800s.
Recently, the
Chandra Observatory observed
Eta Carinae in
X-ray light, adding even more
unanticipated pieces to this enigmatic puzzle.
Pictured above, a horseshoe-shaped outer ring about two
light-years across has been
discovered surrounding a hot core
measuring three light-months across.
One thing appears likely: these structures were caused by
collisions involving matter expelled from the center at supersonic speeds.
Speculation continues that
Eta Carinae will be seen to undergo a
supernova explosion sometime in the next thousand years.
APOD: September 29, 1999 - The Crab Nebula in X Rays
Explanation:
Why does the Crab Nebula
still glow? In the year 1054 A.D. a
supernova
was observed that left a nebula that even today
glows brightly in every color possible, across the entire electromagnetic spectrum.
At the nebula's center is an ultra-dense
neutron star
that rotates 30 times a second.
The power liberated as this
neutron star slows its rotation matches
the power radiated by the
Crab Nebula.
The above picture by the recently launched
Chandra X-Ray Observatory
shows new details of the nebula's center in X-ray light, yielding important clues to how the
neutron star powers the nebula.
Visible are rings of
high-energy particles that are being flung outward near
light-speed from the center, and powerful
jets emerging from the poles.
Astrophysicists continue to study and learn from this
unusual engine
which continually transfers 30 million times more power than
lightning
at nearly perfect
efficiency.
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: July 27, 1999 - Chandra X Ray Telescope
Explanation:
Wrapped in protective blankets and mounted atop an
Inertial Upper Stage (IUS) rocket,
the Chandra X-ray Telescope is
seen in this wide-angle view
before launch snuggled into the
space shuttle Columbia's payload bay.
Columbia's crew released
the telescope, named in honor of the late Nobel Laureate
Subrahmanyan Chandrasekhar,
into orbit on Friday, July 23rd,
where it is now undergoing check out and
activation of its scientific instruments.
To help realize its enormous potential for
exploration of the distant Universe at
X-ray energies, controllers
will perform a series
of firings in the coming days
which will eventually
boost the 10,000 pound telescope into a highly ecentric orbit.
In fact, the final working orbit for Chandra
will range from a close point of about 6,200 miles out
to 87,000 miles or one third of
the distance to the Moon.
The elongated orbit will carry Chandra's
sensitive
X-ray detectors beyond interference caused
by the Earth's
radiation belts allowing Chandra to make about 55 hours
of continuous observations per orbit.
The shuttle Colombia, commanded by
Eileen Collins is
scheduled to land this evening at
11:20 pm EDT at Kennedy Space Center.