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.
illustrates the formation of galaxy clusters and large-scale filaments
in a model of the universe which includes Cold Dark Matter and dark
energy. The frames show the evolution of structures in a 43 million
parsecs (or 140 million light years) box from redshift of z=30 (shortly
after the Big Bang) to the present. |
(Credit: Simulations were performed at the National Center for Supercomputer Applications by Andrey Kravtsov (The University of Chicago) and Anatoly Klypin (New Mexico State University). Visualizations by Andrey Kravtsov.)
(Click on image for 2.4 MB QT movie)
These results were presented at the meeting of
the High Energy Astrophysics Division of the American Astronomical Society
at Mt. Tremblant, Quebec, March 23-26, 2003
"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."
| This Chandra image is of a region called "Lockman Hole North-west", with sky area of ~ 0.5 degree by 0.5 degree, similar to the size of the Moon. The image clearly shows the X-ray sources exhibit lumpiness in the sky.|
(Click on image for larger picture)
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
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.