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Bill Steigerwald 
Goddard Space Flight Center, Greenbelt, Md.     March 25, 2003
William.A.Steigerwald{at}nasa.gov
(Phone: 301/286-5017)

RELEASE NO: 03-34

CHANDRA SEES SHAPE OF UNIVERSE DURING FORMATIVE, ADOLESCENT
YEARS

Scientists using NASA's Chandra X-ray Observatory have
taken a snapshot of the adolescent universe from about
five billion years ago when the familiar web-like structure
of galaxy chains and voids first emerged.

The observation reveals distant and massive galaxies
dotting the sky, clustered together under the gravitational
attraction of deep, unseen pockets of dark matter. This
provides important clues of how the universe matured from
its chaotic beginnings to its elegant structure we see
today.

These results are presented today in a press conference at
the meeting of the High Energy Astrophysics Division of
the American Astronomical Society at Mt. Tremblant, Quebec.

"Piece by piece, we are assembling a photo album of the
universe through the ages," said Yuxuan Yang, a doctorate
candidate at the University of Maryland, College Park,
who conducted the analysis. "Last month we saw a picture
of the infant universe taken with the Wilkinson Microwave
Anisotropy Probe. Now we can add a snapshot of its
adolescence."

The Chandra observation traced a patch of sky known as
the Lockman Hole in the constellation Ursa Major
(containing the Big Dipper). Chandra saw a rich density
of active galaxies, seven times denser than what has
been detected in previous optical and radio surveys at
similar distances. This provides the clearest picture
yet at the large-scale structure of the universe at
such distances (and age), according to Dr. Richard
Mushotzky of NASA Goddard Space Flight Center in
Greenbelt, Md., who led the observation.

If one could capture the universe in a box, scientists
say that the large-scale structure -- that is, galaxies,
galaxy clusters and voids of seemingly empty space --
takes the appearance of a web. Galaxies and intergalactic
gas are strung like pearls on unseen filaments of dark
matter, which comprises over 85 percent of all matter.
Galaxies are attracted to dark matter's gravitational
potential.

Dark matter does not shine, like ordinary matter made
of atoms, and may very well be intrinsically different.
Chandra's observation of distant galaxies in the Lockman
Hole, spread out over several billion light years from
Earth, essentially maps the distribution of dark matter.
This provides clues to how the universe grew.

"We are seeing the universe during its formative years,"
said Mushotzky. "This is billions of years after galaxies
were born, during a period when the universe began to
take on the trappings of an adult."

The galaxies that the team saw with Chandra were either
dim or altogether undetectable with optical and radio
telescopes. This may be because they are enshrouded in
dust and gas, which blocks radio waves and optical light.
X-rays, a higher-energy form of light, can penetrate
this shroud.

"Chandra is the only X-ray telescope with a spatial
resolution comparable to the optical telescopes,"
according to Dr. Amy Barger of University of Wisconsin
at Madison, who led the optical follow-up with the
10-meter Keck telescope on Mauna Kea, Hawaii. "This
is critical to unambiguously identify the optical
counterparts of the X-ray sources and measuring
distances, or redshifts. This allows scientists to
create a three-dimensional image of the large-scale
structure."

The additive effect of future deep and long Chandra
surveys over the next few years will provide an even
sharper picture of the young universe. Other scientists
who participated in this observation include Drs. Len
Cowie and Dave Sanders of the University of Hawaii,
and Ph.D. student Aaron Steffen of the University of
Wisconsin at Madison.

NASA's Marshall Space Flight Center in Huntsville, Ala.,
manages the Chandra program, and TRW, Inc., Redondo
Beach, Calif., is the prime contractor for the spacecraft.
The Smithsonian's Chandra X-ray Center controls science
and flight operations from Cambridge, Mass., for the
Office of Space Science at NASA Headquarters, Washington.

For images, refer to the directory at:
     http://universe.gsfc.nasa.gov/press/largescale/

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