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ASTRONOMERS
IMAGE UNIVERSE'S FIERY YOUTH Like
a hyperactive child, the Universe had an energetic youth, according to a new result
using data from the Two-Micron All Sky Survey (2MASS). Light
emitted by the young Universe, including that from the very first stars and galaxies
to those formed when it was roughly 30 - 40 percent of its current age, has been
detected with the 2MASS survey. The intensity of this light, called the Cosmic
Infrared Background (CIB) radiation, is two to three times what is expected based
on observed galaxies. The
strength of the CIB confirms prior observations indicating that an incredible
burst of star formation occurred during the Universe's youth. It also supports
the idea that a mysterious type of invisible matter pulled gas together shortly
after the Universe's birth, permitting the first stars and galaxies to form. "We
are thrilled to get a glimpse of the youthful Universe, which comes to us from
regions so remote that their details are beyond the reach of the mightiest telescopes
available today," said Dr. Alexander Kashlinsky of Science Systems and Applications,
Inc. at NASA's Goddard Space Flight Center, Greenbelt, Md., who is the lead author
of a paper on this research to be submitted to the Astrophysical Journal. The
results are being announced today by Kashlinsky and his team at the 199th meeting
of the American Astronomical Society in Washington, D.C. The
astronomers used a special set of infrared measurements obtained with the National
Science Foundation's 2MASS survey. This survey was conducted between 1997-2000
by Dr. Michael Skrutskie at the University of Virginia, who is the Principal Investigator
for 2MASS, and Dr. Roc Cutri, the 2MASS Project Scientist at the Infrared Processing
and Analysis Center in Pasadena, California. 2MASS astronomers have cataloged
over 300 million stars and galaxies at wavelengths of light invisible to conventional
optical telescopes. Each
2MASS image is a short exposure, typically just eight seconds long, but some areas
of the sky were electronically photographed as many as 1,000 times. Multiple images
of those regions were combined with a computer, yielding a high-resolution, long-exposure
picture that captured extremely faint objects. The team used these high-quality
pictures, called standard star fields, to detect the weak CIB, which is 500 times
fainter than the night sky. By
carefully combining these images for a small patch of sky in the constellation
Hercules, Dr. Kashlinsky and his team were able to probe the Universe with 100
times the sensitivity of the rest of the sky seen by 2MASS. This was just enough
to begin to detect light from galaxies so far away that only their combined glow
faintly appeared in the infrared images. "What
is exciting about this is that 2MASS never planned to use these particular star
fields to do cosmological studies," says Dr. Sten Odenwald, Chief Scientist
with Raytheon ITS, also at NASA Goddard. "There are dozens of these fields
scattered across the sky, which we can now use to explore the ancient Universe.
It's like exploring Earth's crust by looking down a few deep wells." The
new evidence provides yet another indication that we live in an evolving Universe
as predicted by the prevailing Big Bang theory. "The most important thing
we have confirmed is that, long before Earth formed, the Universe was a lot less
clumpy, but at the same time it was much more active in forming the first stars,"
says Kashlinsky. According
to the team, although the CIB is faint today, the quantity of the CIB radiation
is still between two and three times more than what would be expected if astronomers
just extrapolated based on the amount emitted by observable galaxies. The early
Universe probably experienced a burst of star formation much greater than what
occurs today. As legions of stars turned on, space was flooded with light that
is now seen as an excessively strong CIB. It
wasn't easy to uncover this tell-tale light from the remote Universe. First, the
astronomers had to remove the clutter of hundreds of foreground stars in our Milky
Way galaxy, which covered the tiny patch of sky they were using. Most of the stars
were nearly a million times fainter than those we can see with the naked eye.
They also had to allow for changes in the atmosphere, telescope, and even dust
in our solar system, which could hide the distant cosmic light. What was left
over was a nearly featureless glow that covered their patch of sky. Like
reading a fingerprint, they decoded the clumpy pattern hidden in the light, and
discovered traces of the Universe as it was more than 8 billion years ago. It
was a time in cosmic history when galaxies were already beginning to form clusters,
but the process had not matured to the degree that it has in the modern Universe
around us today. The
measurement showed that the starburst occurred when the Universe was between 5
and 40 percent of its current age (corresponding to a redshift between 7 and 1).
Such a vigorous display so early supports the idea that a strange type of invisible
matter, called cold dark matter, exists. Current
theories about the evolution of the Universe say that the Universe began in an
incredibly tiny, hot, and dense state which quickly expanded and cooled, generating
all the matter and energy that exists. The expansion, called the Big Bang, continues
today. The Big Bang presents a problem for rapid star and galaxy formation, because
stars form when clouds of gas and dust collapse under the influence of their own
self-gravity, and galaxies are born when the mutual gravity of stars causes the
stars to cluster together. Energy,
in the form of electromagnetic radiation (light) from the first instant of the
Big Bang kept normal matter too hot to congregate via gravity. Furthermore, the
expansion of the cosmos increased the space between gas clouds and stars, which
should have inhibited their tendency to come together as stars and galaxies. Cold
dark matter, on the other hand, does not respond to electromagnetic radiation,
which is why it is invisible to us. However, like normal matter, it self-gravitates,
and its gravity pulls on normal matter. Since it did not feel the radiation from
the Big Bang, cold dark matter could have started self-gravitating much earlier
than normal matter. This way, cold dark matter planted gravitational "seeds"
which later attracted normal matter once the Universe cooled sufficiently to allow
normal matter to respond to gravity (about 300,000 years after the Big Bang).
Like a snowball that grows as it rolls down a hill, the seeds continued to attract
ever greater quantities of normal matter, despite the expansion of the cosmos,
and the first stars and galaxies formed relatively soon after the Universe's birth. "A
Universe populated by cold dark matter would be expected to form lots of stars
and galaxies soon after its birth, which is what our result indicates," said
Kashlinsky. The nature of cold dark matter is unknown, but it may be in the form
of exotic sub-atomic particles, or even miniature black holes. More
exciting discoveries may also lie in store for the team of astronomers as they
continue to explore the 2MASS data. Buried within the light detected by 2MASS
may also be glimpses of still more ancient light from the first generations of
stars, or even the light from powerful bursts of star formation concealed by dust
within infant galaxies. NASA's Next Generation Space Telescope, the development
of which is being led by Dr. John Mather at NASA-Goddard, who is also one of the
team members, may be the instrument which will let astronomers explore this next
era in cosmic evolution. The
2MASS project is a collaboration between the University of Massachusetts and the
Infrared Processing and Analysis Center (IPAC) at NASA's Jet Propulsion Laboratory
in Pasadena, Calif. Funding is provided primarily by NASA and the National Science
Foundation. The University of Massachusetts constructed and is maintaining the
observatory facilities, and operates the survey. All data processing and data
product generation is being carried out by IPAC. Survey operations began in Spring
1997 and will last for about 4 years. This work was supported by NASA through
the Office of Space Science via a 1995 Long-Term Space Astrophysics Grant. Back
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