http://www.youtube.com/watch?v=PKjpxdeyzs4&feature=related
http://www.youtube.com/watch?v=HL0waHkIkps
http://www.youtube.com/watch?v=MLoN4MNv90A&feature=endscreen&NR=1
Compact Blue Dwarf Can’t Hide from Hubble
06.15.12
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The NASA/ESA Hubble Space Telescope has captured this view of the dwarf galaxy UGC
5497, which looks a bit like salt sprinkled on black velvet in this image.
The object is a compact blue dwarf galaxy that is infused with newly formed clusters of stars.
The bright, blue stars that arise in these clusters help to give the galaxy an overall bluish
appearance that lasts for several million years until these fast-burning stars explode as
supernovae.
UGC 5497 is considered part of the M 81 group of galaxies, which is located about 12 million
light-years away in the constellation Ursa Major (The Great Bear). UGC 5497 turned up in a
ground-based telescope survey back in 2008 looking for new dwarf galaxy candidates
associated with Messier 81.
According to the leading cosmological theory of galaxy formation, called Lambda Cold Dark
Matter, there should be far more satellite dwarf galaxies associated with big galaxies like the
Milky Way and Messier 81 than are currently known. Finding previously overlooked objects
such as this one has helped cut into the expected tally — but only by a small amount.
Astrophysicists therefore remain puzzled over the so-called "missing satellite" problem.
The field of view in this image, which is a combination of visible and infrared exposures from
Hubble’s Advanced Camera for Surveys, is approximately 3.4 by 3.4 arcminutes.
Image credit: ESA/NASA
Most Quasars Live on Snacks, Not Large Meals
06.19.12
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The galaxies in these four images have so much dust surrounding them that the brilliant
light from their quasars cannot be seen in these Hubble Space Telescope images. Quasars
are the brilliant beacons of light that are powered by black holes feasting on captured
material, and in the process, heating some of the matter to millions of degrees. The images
at top right, bottom left, and bottom right reveal three of the survey's normal-looking
galaxies that host quasars. Only one galaxy in the sample, at top left, shows evidence of an
interaction with another galaxy. The two white blobs are the cores from both galaxies. A
streamer of material, colored brown and blue, also lies below the merging galaxies.The
galaxies existed roughly 8 billion to 12 billion years ago, during a peak epoch of black-hole
growth. The galaxies' masses are comparable to our Milky Way's. The blue patches are
star-forming regions. The brown areas are either dust or old stars. The images were taken
by Hubble's Wide Field Camera 3 between 2011 and 2012. Credit: NASA, ESA, and K.
Schawinski (Yale University)
Black holes in the early universe needed a few snacks rather than one giant meal to fuel their
quasars and help them grow, a new study shows.
Quasars are the brilliant beacons of light that are powered by black holes feasting on captured
material, and in the process, heating some of the matter to millions of degrees. The brightest
quasars reside in galaxies distorted by collisions with other galaxies. These encounters send
lots of gas and dust into the gravitational whirlpool of hungry black holes.
Now, however, astronomers are uncovering an underlying population of fainter quasars that
thrive in normal-looking spiral galaxies. They are triggered by black holes snacking on such
tasty treats as a batch of gas or the occasional small satellite galaxy.
A census of 30 quasar host galaxies conducted with two of NASA's premier observatories, the
Hubble Space Telescope and Spitzer Space Telescope, has found that 26 of the host galaxies
bear no tell-tale signs of collisions with neighbors, such as distorted shapes. Only one galaxy
in the sample shows evidence of an interaction with another galaxy. The galaxies existed
roughly 8 billion to 12 billion years ago, during a peak epoch of black-hole growth.
The study, led by Kevin Schawinski of Yale University, bolsters evidence that most massive
black-hole growth in the early universe was fueled by small, long-term events rather than
dramatic short-term major mergers.
"Quasars that are products of galaxy collisions are very bright," Schawinski said. "The objects
we looked at in this study are the more typical quasars. They're a lot less luminous. The
brilliant quasars born of galaxy mergers get all the attention because they are so bright and
their host galaxies are so messed up. But the typical bread-and-butter quasars are actually
where most of the black-hole growth is happening. They are the norm, and they don't need the
drama of a collision to shine."
Schawinski's science paper has been accepted for publication in a letter to the Monthly
Notices of the Royal Astronomical Society.
For his analysis, Schawinski analyzed galaxies observed by the Spitzer and Hubble telescopes
in the Cosmic Assembly Near-infrared Deep Extragalactic Legacy Survey (CANDELS). He
chose 30 dust-shrouded galaxies that appeared extremely bright in infrared images taken by
the Spitzer telescope, a sign that their resident black holes are feasting on infalling material.
The dust is blocking the quasar's light at visible wavelengths. But infrared light pierces the
dust, allowing Schawinski to study the galaxies' detailed structure. The masses of those
galaxies are comparable to our Milky Way's.
Schawinski then studied the galaxies in near-infrared images taken by Hubble's Wide Field
Camera 3. Hubble’s sharp images allowed careful analysis of galaxy shapes, which would be
significantly distorted if major galaxy mergers had taken place and were disrupting the
structure. Instead, in all but one instance, the galaxies show no such disruption.
Whatever process is stoking the quasars, it's below the detection capability of even Hubble. "I
think it's a combination of processes, such as random stirring of gas, supernovae blasts,
swallowing of small bodies, and streams of gas and stars feeding material into the nucleus,"
Schawinski said.
A black hole doesn't need much gas to satisfy its hunger and turn on a quasar. "There's more
than enough gas within a few light-years from the center of our Milky Way to turn it into a
quasar," Schawinski explained. "It just doesn't happen. But it could happen if one of those
small clouds of gas ran into the black hole. Random motions and stirrings inside the galaxy
would channel gas into the black hole. Ten billion years ago, those random motions were
more common and there was more gas to go around. Small galaxies also were more abundant
and were swallowed up by larger galaxies."
The galaxies in Schawinski's study are prime targets for the James Webb Space Telescope, a
large infrared observatory scheduled to launch later this decade. "To get to the heart of what
kinds of events are powering the quasars in these galaxies, we need the Webb telescope.
Hubble and Spitzer have been the trailblazers for finding them."
For images and more information about this study, visit:
http://hubblesite.org/news/2012/27
For more information about the Hubble Space Telescope, visit:
http://www.nasa.gov/hubble
The Hubble Space Telescope is a project of international cooperation between NASA and the
European Space Agency. NASA's Goddard Space Flight Center in Greenbelt, Md., manages
the telescope. The Space Telescope Science Institute (STScI) in Baltimore, Md., conducts
Hubble science operations. STScI is operated by the Association of Universities for Research
in Astronomy, Inc., in Washington, D.C.
Cheryl Gundy, STScI
Chance Alignment Between Galaxies Mimics a Cosmic Collision
06.14.12
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The NASA/ESA Hubble Space Telescope has produced an incredibly detailed image of a pair of
overlapping galaxies called NGC 3314. While the two galaxies look as if they are in the midst of a
collision, this is in fact a trick of perspective: the two are in chance alignment from our vantage
point. Credit: NASA, ESA, the Hubble Heritage Team (STScI/AURA)-ESA/Hubble Collaboration, and
W. Keel (University of Alabama)
NASA's Hubble Space Telescope shows a rare view of a pair of overlapping galaxies, called NGC 3314.
The two galaxies look as if they are colliding, but they are actually separated by tens of millions of
light-years, or about ten times the distance between our Milky Way and the neighboring Andromeda
galaxy. The chance alignment of the two galaxies, as seen from Earth, gives a unique look at the
silhouetted spiral arms in the closer face-on spiral, NGC 3314A.
The motion of the two galaxies indicates that they are both relatively undisturbed and that they are
moving in markedly different directions. This indicates they are not on any collision course. NGC
3314A's warped shape is likely due to an encounter with another nearby galaxy, perhaps the large
spiral galaxy NGC 3312 (located outside the Hubble image).
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This image shows a wide field of view around the overlapping galaxy pair NGC 3314. While the two
galaxies look as if they are in the midst of a collision, this is in fact a trick of perspective: the two
are in chance alignment from our vantage point. Credit: NASA, ESA, Digitized Sky Survey 2
(Acknowledgement: Davide de Martin)
Because of the alignment, NGC 3314B's dust lanes appear lighter than those of NGC 3314A. This is
not because that galaxy lacks dust, but rather because its dust lanes are lightened by the bright fog of
stars in the foreground. NGC 3314A's dust, in contrast, is backlit by the stars of NGC 3314B,
silhouetting them against the bright background.
The color composite was produced from exposures taken in blue and red light with Hubble's
Advanced Camera for Surveys. The pair of galaxies lie roughly 140 million light-years from Earth, in
the direction of the southern hemisphere constellation Hydra.
Credit: NASA, ESA, the Hubble Heritage Team (STScI/AURA)-ESA/Hubble Collaboration, and W. Keel
(University of Alabama)
The Sagittarius Dwarf Galaxy
This dwarf galaxy is the nearest galaxy to our own. However, it was only discovered as
recently as 1994. It lies on the far side of the galaxy from us and is heavily obscured by the
intervening gas, dust and stars. It is approximately 78000 light years away and about 10000
light years in diameter. It is orbiting our galaxy in a period of about 1 billion years but it
cannot be expected to last much longer, in a few hundred million years it will be ripped apart
by our own galaxy. It contains about one hundred million stars. It also lies in roughly the
same position as the globular cluster M54 but whether this globular cluster is actually part of
the dwarf galaxy is unclear.