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:
