NASA's Hubble Space Telescope is providing a new perspective on the
remote universe, including new views of young and distant galaxies
bursting with stars. Scientists described the findings Tuesday in a news
conference sponsored by the American Astronomical Society (AAS).
Highlighted in the briefing were three discoveries -- four unusually
bright galaxies as they appeared 13 billion years ago, the deepest image
ever obtained of a galaxy cluster, and a sampling of galaxies thought
to be responsible for most of the stars we see today.
The ultra-bright, young galaxies, discovered using data from NASA's
Hubble and Spitzer space telescopes, are bursting with star formation
activity, which accounts for their brilliance. The brightest one is
forming stars approximately 50 times faster than our Milky Way galaxy
does today. These fledgling galaxies are only one-twentieth the size of
the Milky Way, but they probably contain about 1 billion stars crammed
together.
Although Hubble has previously identified galaxies at this early
epoch, astronomers were surprised to find objects that are about 10 to
20 times more luminous than anything seen previously.
"These just stuck out like a sore thumb because they are far brighter
than we anticipated," explained Garth Illingworth of the University of
California at Santa Cruz. "There are strange things happening regardless
of what these sources are. We're suddenly seeing luminous, massive
galaxies quickly build up at such an early time. This was quite
unexpected."
The galaxies were first detected with Hubble. Its sharp images are
crucial to finding such distant galaxies and enabled the astronomers to
measure their star-formation rates and sizes. Using Spitzer, the
astronomers were able to estimate the stellar masses by measuring the
total stellar luminosity of the galaxies.
"This is the first time scientists were able to measure an object's
mass at such a huge distance," said Pascal Oesch of Yale University in
New Haven, Conn. "It's a fabulous demonstration of the synergy between
Hubble and Spitzer."
The result bodes well for NASA's James Webb Space Telescope,
currently in development. Scientists anticipate using Webb to look even
farther back in time to find young, growing galaxies as they existed
only a few hundred million years after the universe began in theorized
big bang.
An unprecedented long distance view of the universe comes from an
ambitious collaborative project with Hubble called The Frontier Fields.
It is the longest and deepest exposure obtained to date of a cluster of
galaxies, and shows some of the faintest and youngest galaxies ever
detected. The image contains several hundred galaxies as they looked 3.5
billion years ago.
Appearing in the foreground of the image is Abell 2744, a massive
galaxy cluster located in the constellation Sculptor. The immense
gravity in Abell 2744 is being used as a lens to warp space and brighten
and magnify images of more distant background galaxies. The more
distant galaxies appear as they did longer than 12 billion years ago,
not long after the big bang.
The Hubble exposure reveals almost 3,000 of these background galaxies
interleaved with images of hundreds of foreground galaxies in the
cluster. Their images not only appear brighter, but also smeared,
stretched and duplicated across the field. Because of the gravitational
lensing phenomenon, the background galaxies are magnified to appear as
much as 10 to 20 times larger than they would normally appear.
Furthermore, the faintest of these highly magnified objects is 10 to 20
times fainter than any galaxy observed previously. Without the boost
from gravitational lensing, the many background galaxies would be
invisible.
The Hubble exposure will be combined with images from Spitzer and
NASA's Chandra X-ray Observatory to provide new insight into the origin
and evolution of galaxies and their accompanying black holes.
Hubble also uncovered a substantial population of 58 young,
diminutive galaxies that scientists long suspected were responsible for
producing a majority of stars now present in the cosmos during the
universe's early years.
Deep exposures in ultraviolet light, made with Hubble's Wide Field
Camera 3, revealed a sampling of galaxies that existed more than 10
billion years ago, when the universe was roughly 3.4 billion years old.
They are the smallest, faintest, galaxies seen in the remote universe to
date. A census of galaxies existing at the time indicates these small,
faint galaxies are 100 times more abundant in the universe than their
more massive cousins.
"There's always been a concern that we've only found the brightest of
the distant galaxies," said Brian Siana of the University of California
at Riverside. "The bright galaxies, however, represent the tip of the
iceberg. We believe most of the stars forming in the early universe are
occurring in galaxies we normally can't see at all. Now we have found
those 'unseen' galaxies, and we're really confident that we're seeing
the rest of the iceberg."
Normally too faint for Hubble to see, these galaxies were revealed
through gravitational lensing focused on a massive galaxy cluster known
as Abell 1689 in the constellation Ursa Major. The cluster magnified
light emitted by distant objects behind it, causing the newly discovered
galaxies to appear bigger and brighter. If this sample is
representative of the entire population at the time, then the majority
of new stars formed in such small, unseen galaxies.
"Though these galaxies are very faint, their increased numbers mean
that they account for the majority of star formation during this epoch,"
said team member Anahita Alavi, also of the University of California at
Riverside.
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