Astronomy Picture of the Day |
APOD: 2008 November 9 - Two Black Holes Dancing in 3C 75
Explanation:
What's happening at the center of active galaxy 3C 75?
The two bright sources at the center of
this
composite x-ray (blue)/
radio
(pink) image are co-orbiting supermassive black holes powering
the giant radio source
3C 75.
Surrounded by multimillion degree
x-ray emitting gas, and
blasting out jets of relativistic particles the
supermassive black holes
are separated by 25,000 light-years.
At the cores of
two merging galaxies in the
Abell 400
galaxy cluster they are some 300 million light-years away.
Astronomers conclude that these two supermassive
black
holes are bound together by gravity in a binary system
in part because
the jets' consistent swept back appearance is most likely due to their
common motion as they speed through the hot cluster gas
at 1200 kilometers per second.
Such spectacular cosmic mergers
are thought to be common in crowded
galaxy cluster environments in the distant universe.
In their final stages the mergers are expected to be intense sources of
gravitational waves.
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 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 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: 2006 November 29 - A Big Dish at the VLA Radio Observatory
Explanation:
They are so large, they are almost unreal.
The radio dishes of the
Very Large Array (VLA) of
radio telescopes
might appear to some as a strange combination of a dinosaur skeleton and common
satellite-TV receiving dish.
Together, the 27 dishes of the
VLA
combine high sensitivity with high resolution,
enabling a series of important astronomical discoveries, including
water ice on planet Mercury,
micro-quasars in our Galaxy,
gravitationally-induced Einstein rings around distant galaxies, and
radio counterparts to cosmologically distant gamma-ray bursts.
Pictured above, a dish from the VLA was photographed last week near
Socorro,
New Mexico,
USA.
APOD: 2006 June 2 - IC 443: Supernova Remnant and Neutron Star
Explanation:
IC 443 is typical of the
aftermath
of a stellar explosion, the ultimate fate of massive stars.
Seen in this
false-color composite image, the
supernova remnant is still glowing
across the spectrum,
from radio (blue) to optical (red) to x-ray (green) energies --
even though light from the stellar
explosion that created the expanding cosmic cloud first
reached planet Earth thousands of years ago.
The odd thing about IC 443 is the apparent
motion of its dense
neutron star, the collapsed remnant of the
stellar core.
The close-up inset shows the swept-back wake created as the neutron star
hurtles
through the hot gas, but that direction
is not aligned with the direction toward the apparent center of
the remnant.
The misalignment suggests that the
explosion site was offset
from the center or that fast-moving gas in the nebula has
influenced the wake.
The wide view of IC 443, also known as the
Jellyfish nebula,
spans about 65 light-years at the supernova remnant's
estimated distance of 5,000 light-years.
APOD: 2006 May 14 - The Very Large Array of Radio Telescopes
Explanation:
The most photogenic array of
radio telescopes in the world has also
been one of the most productive.
Each of the 27
radio telescopes in the
Very Large Array (VLA) is the size of a
house and can be moved on train tracks.
The above pictured
VLA, inaugurated in
1980 is situated in
New Mexico,
USA.
The VLA has been used to discover
water on planet Mercury,
radio-bright coronae around ordinary stars,
micro-quasars in our Galaxy,
gravitationally-induced Einstein rings around distant galaxies, and
radio counterparts to cosmologically distant gamma-ray bursts.
The vast size of the
VLA has allowed astronomers to study the
details of super-fast cosmic jets, and even
map the center of our Galaxy.
An upgrade of the VLA is
being planned.
APOD: 2006 April 27 - NGC 4696: Energy from a Black Hole
Explanation:
In many cosmic environments,
when material falls toward
a black hole energy is produced as some of the matter is
blasted back out in jets.
In fact, such black hole "engines" appear to be the most
efficient in the Universe, at least on a galactic scale.
This
composite image
illustrates one example of an
elliptical galaxy with an efficient
black hole engine, NGC 4696.
The large galaxy is the brightest member of the
Centaurus
galaxy cluster, some 150 million light-years away.
Exploring
NGC 4696
in x-rays (red) astronomers
can measure the rate at which infalling matter fuels the
supermassive black hole and compare
it to the energy output in the jets to
produce giant radio emitting bubbles.
The bubbles, shown here in blue, are about 10,000
light-years across.
The results confirm
that the process is much more efficient
than producing energy through
nuclear
reactions - not to mention
using fossil fuels.
Astronomers also suggest that as the black hole
pumps out energy and heats the surrounding gas, star formation
is ultimately shut off, limiting the size of large galaxies like
NGC 4696.
APOD: 2006 April 12 - Binary Black Hole in 3C 75
Explanation:
The two bright sources at the center of
this
composite x-ray (blue)/
radio
(pink) image are co-orbiting supermassive black holes powering
the giant radio source
3C 75.
Surrounded by multimillion degree x-ray emitting gas, and
blasting out jets of relativistic particles the
supermassive black holes
are separated by 25,000 light-years.
At the cores of
two merging galaxies in the
Abell 400
galaxy cluster they are some 300 million light-years away.
Astronomers
conclude that these two supermassive
black
holes are bound together by gravity in a binary system
in part because
the jets' consistent swept back appearance is most likely due to their
common motion as they speed through the hot cluster gas
at 1200 kilometers per second.
Such spectacular cosmic mergers are thought to be common in crowded
galaxy cluster environments
in the distant universe.
In their final stages the mergers are expected to be intense
sources of gravitational waves.
APOD: 2005 June 28 - The Giant Radio Lobes of Fornax A
Explanation:
Together, the radio lobes span over one million light years --
what caused them?
In the center is a large but peculiar elliptical galaxy dubbed
NGC 1316.
Detailed inspection of the
NGC 1316 system indicates that
it began absorbing a
small neighboring galaxy
about 100 million years ago.
Gas from the
galactic collision has fallen inward toward the massive central
black hole, with
friction
heating the gas to 10 million degrees.
For reasons not yet well understood, two oppositely pointed
fast moving jets of
particles then developed, eventually smashing
into the ambient material on either side of the giant
elliptical galaxy.
The result is a huge reservoir of hot gas that emits
radio waves, observed as the orange (false-color)
radio lobes in the
above image.
The radio image is superposed on an
optical survey image of the same part of the sky.
Strange patterns in the radio lobes likely indicate
slight changes in the directions of the jets.
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: 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: 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 May 28 - The Very Large Array of Radio Telescopes
Explanation:
The most photogenic array of
radio telescopes in the world has also
been one of the most productive.
Each of the 27
radio telescopes in the
Very Large Array (VLA) is the size of a
house and can be moved on train tracks.
The above pictured
VLA, celebrating its
twenty-second year of operation, is situated in
New Mexico,
USA.
The VLA has been used to discover
water on planet Mercury,
radio-bright coronae around ordinary stars,
micro-quasars in our Galaxy,
gravitationally-induced Einstein rings around distant galaxies,
and
radio counterparts to cosmologically distant gamma-ray bursts.
The vast size of the
VLA has allowed astronomers to study the
details of super-fast cosmic jets, and even
map the center of our Galaxy.
An upgrade of the VLA is
being planned.
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: 2001 September 5 - 3C175: Quasar Cannon
Explanation:
3C175 is not only a quasar, it is a galaxy-fueled particle cannon.
Visible as the central dot is
quasar 3C175, the
active center of a galaxy so distant that the light we see from it was emitted when the
Earth was
just forming.
The
above image was recorded in
radio waves by an array of house-sized telescopes
called the Very Large Array (VLA).
Shooting out from 3C175 is a thin
jet of
protons and electrons
traveling near the
speed of light that is over one million
light-years long.
The jet acts like a
particle cannon and bores through
gas cloud in its path.
How this
jet forms and why it is so narrow remain
topics of
current
research.
APOD: 2001 June 14 - Around The Arches Cluster
Explanation:
The most compact cluster of stars known in our galaxy,
the Arches cluster, boasts 100 or so massive, young
stars contained within a diameter of one light-year.
Seen toward the
constellation Sagittarius, the
Arches cluster is
about 25,000 light-years from planet
Earth and lies within a scant 100 light-years of
the supermassive black hole believed to lurk
in our Milky Way Galaxy's center.
This
combination of images in
radio,
infrared, and
x-ray light
illustrates this star cluster's bizarre galactic neighborhood.
Shown
in red, radio emission traces the filamentary arching
structures near
the galactic center around the
Arches cluster location.
Within the zoomed inset box, infrared image data shows some of
the cluster's individual stars as bright point-like sources.
The diffuse emission in blue surrounding the cluster stars is a
false-color
x-ray image of an enveloping cloud of 60 million degree
gas -- the
first time such an energetic star cluster halo has
been detected.
Astronomers
consider the tightly packed and relatively nearby Arches cluster,
an analog of the furious star forming regions
in galaxies
millions of light-years away.
APOD: 2001 June 3 - A GRB 000301C Symphony
Explanation:
Last March, telescopic instruments in Earth and space tracked
a tremendous explosion that occurred across the universe.
A nearly unprecedented symphony of international observations began
abruptly on 2000 March 1 when Earth-orbiting
RXTE,
Sun-orbiting
Ulysses,
and asteroid-orbiting
NEAR
all
detected
a 10-second
burst of high-frequency
gamma radiation.
Within 48 hours astronomers using the 2.5-meter
Nordic Optical Telescope
chimed in with the observation of a middle-frequency
optical counterpart
that was soon confirmed with the 3.5-meter
Calar Alto Telescope in Spain.
By the next day the explosion was picked up in low-frequency
radio waves by the by the European
IRAM 30-meter dish in Spain,
and then by the
VLA telescopes in the US.
The Japanese 8-meter
Subaru Telescope interrupted a
maiden engineering test to trumpet in
infrared observations.
Major telescopes across the globe soon began
playing along as
GRB 000301C came into view, detailing
unusual behavior.
The
Hubble Space Telescope
captured the
above image and was the first to
obtain an accurate distance to the explosion,
placing it near redshift 2, most of the way across the visible
universe.
The Keck II Telescope in Hawaii quickly
confirmed and refined the redshift.
Even today, no one is sure what
type of explosion
this was.
Unusual features of the light curve
are still being studied, and no
host galaxy
appears near the position of this explosion.
APOD: 2000 May 30 - The Very Large Array Turns Twenty
Explanation:
The most photogenic array of
radio telescopes in the world has also
been one of the most productive.
Each of the 27
radio telescopes in the
Very Large Array (VLA) is the size of a
house and can be moved on train tracks.
The VLA, celebrating its
twentieth year of operation, is
pictured above in a compact formation in front of
Tres Montosas,
New Mexico,
USA.
The VLA has been used to discover
water on planet Mercury,
radio-bright coronae around ordinary stars,
micro-quasars in our Galaxy,
gravitationally-induced Einstein rings around distant galaxies,
and
radio counterparts to cosmologically distant gamma-ray bursts.
The vast size of the
VLA has allowed astronomers to study the
details of super-fast cosmic jets, and even
map the center of our Galaxy.
An upgrade of the VLA is being planned.
APOD: 2000 March 14 - A GRB 000301C Symphony
Explanation:
Telescopic instruments in Earth and space are still tracking
a tremendous explosion that occurred across the universe.
A nearly unprecedented symphony of international observations began
abruptly on March 1 when Earth-orbiting
RXTE,
Sun-orbiting
Ulysses,
and asteroid-orbiting
NEAR
all
detected
a 10-second
burst of high-frequency
gamma radiation.
Within 48 hours astronomers using the 2.5-meter
Nordic Optical Telescope
chimed in with the observation of a middle-frequency
optical counterpart
that was soon confirmed with the 3.5-meter
Calar Alto Telescope in Spain.
By the next day the explosion was picked up in low-frequency
radio waves by the by the European
IRAM 30-meter dish in Spain,
and then by the
VLA telescopes in the US.
The Japanese 8-meter
Subaru Telescope interrupted a
maiden engineering test to trumpet in
infrared observations.
Major telescopes across the globe soon began
playing along as GRB 000301C came into view, detailing
unusual behavior.
The
Hubble Space Telescope
captured the
above image and was the first to
obtain an accurate distance to the explosion,
placing it near redshift 2, most of the way across the visible
universe.
The Keck II Telescope in Hawaii quickly
confirmed and refined the redshift.
Still, no one is sure what
type of explosion
this was.
The symphony is not over - oddly no
host galaxy
appears near the position of this explosion.
Will one appear as the din of the loud
fireball fades?
APOD: 2000 January 17 - V4641 Sgr: The Closest Black Hole Candidate
Explanation:
An object many astronomers believe is a
black hole has been found only 1500
light-years from Earth,
making it the closest
black hole candidate.
Although dramatic explosions emanate from the object,
it is far enough away so that we are in no danger.
Pictured above, V4641 was imaged just after
emitting an outburst in the radio band.
Jets, which lasted only minutes, are visible.
V4641 is the fourth known
microquasar, a miniature version of the massive, matter spewing
black holes thought to exist in the
centers of galaxies.
The explosions are not thought to emanate from within the
black hole, a location where neither matter
nor information can escape, but from around the
black hole, where matter from its companion star may
be heating up as it falls in.
Astronomers are
working to understand why
V4641 acts strangely even for a
black hole, as the
explosions it creates fade within minutes,
and appear at different times in
different bands of light.
APOD: August 23, 1999 - Sundogs over the VLA
APOD: June 20, 1999 - A Very Large Array of Radio Telescopes
APOD: February 16, 1999 - The Large and Small of M87
APOD: July 27, 1997 - A Very Large Array of Radio Telescopes
APOD: June 21, 1996 - A Very Large Array of Radio Telescopes
APOD: September 30, 1995 - An Energetic Radio Galaxy
Explanation:
What if you woke up one morning and saw
more than one Sun in the sky?
Most probably, you would be seeing sundogs, extra-images of the
Sun created by falling
ice-crystals in the Earth's atmosphere.
As water freezes in the atmosphere,
small, flat, six-sided,
ice crystals might be formed.
As these crystals flutter to the ground,
much time is spent with their faces flat, parallel to the ground.
An observer may pass through the same plane as many of the
falling ice crystals near sunrise or sunset.
During this alignment, each crystal can act like a miniature lens,
refracting sunlight into our view and creating
parhelia,
the technical term for sundogs.
Sundogs were
Explanation:
Pictured above is one of the world's premiere radio astronomical
observatories: The
Very
Large Array (VLA). Each antenna dish is as big as a
house
(25 meters across) and mounted on
railroad tracks.
The VLA consists of 27 dishes - together capable of
spanning the size of a city (35 kilometers). The
VLA
is the most sensitive
radio telescope ever, and, through
interferometry, can resolve a golf ball-sized radio source 150
kilometers away (0.04 arcsec).
The
VLA
is continually making new
discoveries, including determining the
composition
of galaxies,
passing
comets, quasars,
HII regions, and
clusters of galaxies.
The VLA is also used to receive the
weak
radio signals broadcast from interplanetary
spacecraft. The VLA is located in
New Mexico, USA. A
significant upgrade of VLA's capabilities is planned.
Explanation:
The small core of
elliptical galaxy M87
appears to be energizing its whole galactic neighborhood.
Recent images from the
Very Large Array (VLA) of
radio telescopes indicate that huge bubbles of
hot gas not only exist but are still being created.
These bubbles measure 200,000 light-years across
and surround the
entire galaxy.
The source creating and feeding the bubbles
has been traced to jets pointing back to
M87's center, where a
supermassive black hole
is thought to live. The smallest scale on the
above radio-map is 0.2 light-years and imaged by
many radio telescopes working together (VLBI).
The labeled numbers
refer to the wavelength of the radio waves observed.
The exact composition of these jets is not known, but thought to contain various
subatomic particles.
Explanation:
Pictured above is one of the world's premiere radio astronomical
observatories: The
Very
Large Array (VLA). Each antenna dish is as big as a
house
(25 meters across) and mounted on
railroad tracks. The VLA consists
of 27 dishes - together capable of spanning the size of a city (35
kilometers). The
VLA
is the most sensitive
radio telescope ever, and, through
interferometry, can resolve a golf ball-sized radio source 150
kilometers away (0.04 arcsec). The
VLA
is continually making new
discoveries, including determining the
composition
of galaxies,
passing
comets,
quasars,
HII regions,
and
clusters of galaxies. The VLA is also
used to receive the
weak
radio signals broadcast from interplanetary
spacecraft. The VLA is located in
New Mexico, USA. A
significant
upgrade of VLA's capabilities is planned.
Explanation:
Pictured above is one of the world's premiere radio astronomical
observatories: The
Very
Large Array (VLA). Each antenna dish is as big as a
house
(25 meters across) and mounted on
railroad tracks. The VLA consists
of 27 dishes - together capable of spanning the size of a city (35
kilometers). The
VLA
is the most sensitive
radio telescope ever, and, through
interferometry, can resolve a golf ball-sized radio source 150
kilometers away (0.04 arcsec). The
VLA
is continually making new
discoveries, including determining the
composition
of galaxies,
passing
comets,
quasars,
HII regions,
and
clusters of galaxies. The VLA is also
used to receive the
weak
radio signals broadcast from interplanetary
spacecraft. The VLA is located in
New Mexico, USA. A
significant
upgrade of VLA's capabilities is planned.
Explanation:
The radio and optical emission seen in the above superposed images of the
radio galaxy 3C368 indicate that energetic
processes are at work. A radio
galaxy is a
galaxy
that is visible to radio telescopes. A large radio
signal usually indicates very powerful phenomena. The optical light is
shown above in red and the radio emission in blue contours. Currently, one
can only guess what causes the unusual radio and optical features.
Scientists working with the
Hubble Space Telescope
speculate
that the radio emission might have resulted from jets of high-velocity
material thrown off from the center of the galaxy, while the optical light
comes from gas and
dust
that are remnants of a burst of star formation triggered by the radio
jet.
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