- Astronomers using the Hubble Space Telescope (HST) unveiled
the deepest look into the universe yet, a portrait of what could be the
most distant galaxies ever seen.
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- The new image, called the Hubble Ultra Deep Field (HUDF),
includes objects that until now have been too faint to be seen and includes
ancient galaxies that emerged just 700 million years after the Big Bang
from what astronomers call the "dark ages" of the universe.
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- "This image is the deepest view in the visible that
we've ever taken, where an object about as bright as a firefly on the Moon
would be visible," said Massimo Stiavelli, of the Space Telescope
Science Institute (STScI) in Baltimore and the UHDF project leader.
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- Stiavelli said the new image is six times more sensitive
than previous deep sky surveys and four times better than even Hubble's
last faraway looks, the Hubble Deep Fields (HDFs), taken in 1995 and 1998.
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- "It has these extra colors with extra red shifts,
which leads you to the end of the dark ages, something you couldn't do
with the HDF," he added.
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- The HUDF field contains an estimated 10,000 galaxies
in a patch of sky in the constellation Fornax, a region just below the
constellation Orion, that appears in an area of the sky that appears largely
empty if observed by ground-based instruments. The image is about one-tenth
the diameter of the full moon and took Hubble one million seconds to take.
To cover the entire sky with such detail would take the HST one million
years, astronomers said.
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- The HUDF is the result of two separate exposures, one
taken by Hubble's Advanced Camera for Surveys (ACS) and the other by the
Near Infrared Camera and Multi-object Spectrometer (NICMOS). By combining
the two, astronomers can search for galaxies that existed between 800 and
400 million years after the Big Bang. But it's the NICMOS instrument that
will reveal the farthest galaxies ever seen, because only it can detect
light stretched past the visible, which is ACS territory, far into the
near-infrared spectrum.
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- Astronomers can tell how old a galaxy is by measuring
the light it emits, specifically the amount of light that has been shifted
toward the red end of the spectrum. The higher red shift a galaxy has,
the more distant it is and the earlier it existed in the universe.
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- Hubble researchers are confident their new image contains
galaxies whose light has been stretched to a red shift of 6 or more. There's
even a good case that it contains ancient galaxies of red shift 12, which
would place them about 300 million years after the Big Bang.
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- Mario Livio, head of the Institute Science Division at
STScI, says that if red shift 12 galaxies are indeed in the image, they
will be found soon. "It could happen this afternoon," Livio told
SPACE.com in an interview prior to the Hubble announcement. "That
might be stretching it a bit, but it will be easy."
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- Stiavelli, head of ultra deep field observations, said
that finding a red shift 12 galaxy will be important because it will be
done not with a gravitational lens, but "by brute force." Gravitational
lenses, which use the gravitational fields of nearby objects to magnify
those in the background, have helped ground observers detect galaxies dating
back to just 500 million years post-Big Bang. But the natural zoom view
is rare.
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- STScI astronomers said the ACS image contained a wide
range of regular galaxies, including spirals, ellipticals, as well as a
number of oddball galaxies, some of which appear to be interacting with
one another. Some of the galaxies look like toothpicks, while others are
arranged like links on a bracelet.
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- "We can now see tidal tails, wisps of gas, that
cover large distances," Stiavelli said, adding that there are some
interaction effects that defy identification, include some very red, very
strange objects. "We don't know exactly what this is."
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- "This will have a lot of impact on the James Webb
Space Telescope (JWST), since it's tasked with studying this period at
even higher sensitivity," said Rodger Thompson of the University of
Arizona and the NICMOS principal investigator. Scheduled for launch in
2011, the JWST is to be Hubble's successor and pick up where the HST left
off.
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- Hubble's ACS picture required a series of exposures taken
over the course of 400 HST orbits around Earth from Sept. 24, 2003, to
Jan. 16, 2004. About the size of a phone booth, ACS captured ancient photons
of light that began traversing the universe even before Earth existed.
Photons of light from the very faintest objects arrived at a trickle of
one photon per minute, as opposed to millions of photons per minute from
nearer galaxies.
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- The entire HUDF was observed with the advanced camera's
"grism" spectrograph, an instrument used to measure distances
to these distant objects.
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- "We hope, in the next few months, to not get much
sleep and analyze this data to see what's happening in the universe,"
said Sangeeta Malhotra of the STScI and principal investigator for the
Ultra Deep Field's ACS grism follow-up study. Already, the grism spectra
has yielded the identification of about 1,000 objects, including some prime
candidates for distant galaxies, which appear as intensely faint, red points
of light.
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- Based on those identifications, some of these objects
are among the farthest and youngest galaxies ever seen, said Malhotra,
adding that the grism spectra also distinguish among other types of very
red objects, such as old and dusty red galaxies, quasars and cool dwarf
stars.
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- Astronomers are eager to see the Hubble receive a stay
of execution in the form of future servicing missions by NASA 's space
shuttles to extend the telescope's lifetime. Adam Riess, a supernova researcher
for STScI, said an extension could help astronomers find supernova early
in the universe's lifetime.
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- "There are no supernovae in this deep field, but
the results show that supernova in the early universe could be found if
Hubble could be extended," Riess said. "Those could provide valuable
insight into dark energy and fate of the universe."
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- The STScI is operated by the Association of Universities
for Research in Astronomy, Inc. under contract with NASA's Goddard Space
Flight Center, Greenbelt, Md. The HST is a project of international cooperation
between NASA and the European Space Agency.
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