From: Spudboy100@aol.com
Date: Fri Aug 02 2002 - 00:47:01 MDT
http://washingtontimes.com/upi-breaking/20020801-051114-9603r.htm
Discovery sheds light on dark matter
CAMBRIDGE, Mass., Aug. 1 (UPI) -- Four independent teams of scientists
have found massive filaments of hot gas that snake through the universe like
an intergalactic web and may lead to new clues about the mysterious substance
called dark matter.
The gas filaments not only account for many times the material that is
contained in all the visible stars and galaxies, but they also suggest where
even more matter might be found because the gas clouds seem to have been
shaped by rivers of gravity, the scientists said.
At present, no one can account for more than about 10 percent of the
matter cosmologists say is necessary to allow the gravitational behavior of
the universe. For example, the clusters of stars that comprise most galaxies
should not be able to clump together at the speeds at which they orbit
galactic cores. The rest of the universe apparently is composed of dark
matter, which so far has remained shielded from view.
The new findings, from the orbiting Chandra X-ray Observatory -- a
less-well-known cousin of the Hubble Space Telescope that studies the
universe in wavelengths beyond those of visible light -- could provide
valuable insight into the location of the missing mass because cosmologists
think the gas filaments were formed by the gravitational influence of dark
matter.
"These observations are a major advance in our understanding of how the
universe evolved over the last 10 billion years," said Fabrizio Nicastro, who
heads the Harvard-Smithsonian Center for Astrophysics.
Researchers used two different techniques to find the gas clouds, which
range in temperature from about 300,000 degrees Celsius to 5 million degrees.
One method was to study X-ray emissions from distant quasars -- the strange
and immensely powerful objects that seem to populate the most distant parts
of the universe -- to determine how much energy was being absorbed by oxygen
and other elements in the gas clouds as the emissions passed through.
By measuring how much the X-rays "dimmed," astronomers could estimate
the temperature, density and mass of the absorbing gas clouds.
The second technique was to study the absorption of X-rays by a
foreground galaxy, enabling researchers to deduce the presence of hot gas
behind the galaxy. In doing so, they discovered both our Milky Way and the
neighboring Andromeda galaxies are embedded in one of the filaments. This
fact gives a sense of the size of the filaments because the one weaving its
way through the two galaxies is estimated to be several billion light-years
long.
Joel Bregman, with the astronomy department at the University of
Michigan in Ann Arbor, used medical terms to describe the process by which
the filaments were detected. "Normally the doctor studies the X-ray shadow
produced by your bones to learn about your bones," he said. "In essence, we
used the shadow to learn about the X-ray machine."
The researchers have asked for additional observing time on the Chandra
Observatory to confirm the findings, said Smita Mathur, with Ohio State
University in Columbus.
"That would be about the limit of what we can do with Chandra," Mathur
told United Press International. To produce detailed maps of the gas,
astronomers are going to need a more powerful X-ray telescope, she said, such
as the proposed Constellation-X observatory -- a quartet of orbiting
instruments whose combined sensing ability will be 100 times greater than
Chandra's.
"Computer simulations have been telling us for several years that most
of the 'missing' gas in the universe should be in hot filaments," said
Mathur. "Most of those filaments are too faint to see, but it looks like we
are finally finding their shadows."
The teams report their research in four articles in the Aug. 1 issue of
Astrophysical Journal.
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(Reported by Irene Brown, UPI Science News, at Cape Canaveral, Fla.)
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