Posted on 08/02/2002 4:41:48 PM PDT by vannrox
Reprinted from ScienceDaily Magazine ...
Source: NASA/Marshall Space Flight Center
Date Posted: Thursday, August 01, 2002
Web Address: http://www.sciencedaily.com/releases/2002/08/020801080835.htm
"The Chandra observations, together with ultraviolet observations, are a major advance in our understanding of how the universe evolved over the last 10 billion years," said Fabrizio Nicastro, leader of Harvard-Smithsonian Center for Astrophysics (CfA) in Cambridge, Mass., and head of one of the teams of scientists involved in the discovery.
Four independent teams of scientists, whose results appear as separate papers in the Astrophysical Journal, used Chandra to detect intergalactic gas with temperatures ranging from 300,000 to 5 million degrees Celsius. This gas forms part of a gigantic system of hot gas and dark matter that defines the cosmic landscape. The gaseous component alone contains more material than all the stars in the universe.
"We had strong suspicions from the Big Bang theory and observations of the early universe that this gas exists in the present era, but like a stealth aircraft it had eluded our detection," said Claude Canizares of the Massachusetts Institute of Technology (MIT), Cambridge, who along with Taotao Fang, also of MIT, led of one of the teams.
The hot gas detected by Chandra can be used to trace the presence of the more massive dark-matter component. The discovery of the hot gas may eventually enable astronomers to map the distribution of dark matter in the universe and perhaps understand its origin.
Ultraviolet telescopes had detected cooler components of the hot gas system, but because of its high temperatures most of it is detectable only with an extremely sensitive X-ray telescope. The various groups used two techniques to probe the intergalactic gas. One method uses the absorbing effects of the gas on X-rays from distant galaxies.
On their way to Earth, the X-rays from a distant quasar dim as they pass through a cloud of the intergalactic gas. By measuring the amount of dimming due to oxygen and other elements in the cloud, astronomers were able to estimate the temperature, density and mass of the absorbing gas.
Observations of the quasars PKS 2155-304 by the MIT and Harvard-Smithsonian groups, and H1821+643 by a group from Ohio State, Columbus, revealed various parts of the hot gas system. One of these appears to be a filament in which the Milky Way and Andromeda galaxies are embedded, whereas other detected portions are at distances of a few billion light- years from Earth.
These results confirm earlier work by Joel Bregman and Jimmy Irvin of the University of Michigan in Ann Arbor, who flipped the normal procedure, and used the fact that the hot gas is itself a source of X-rays. By observing the absorption of X- rays from the hot gas by a foreground galaxy, they were able to deduce the presence of hot gas behind the galaxy.
"Normally the doctor studies the X-ray shadow produced by your bones to learn about your bones," said Bregman. "In essence, we used the shadow to learn about the X-ray machine."
During the first few billion years of the universe, about 20 percent of the matter came together under the influence of gravity to form groups and clusters of galaxies. Theories predict that most of the remaining normal matter and dark matter formed an immense filamentary web connecting the groups and clusters of galaxies, predicted to be so hot that it would be invisible to optical, infrared and radio telescopes.
"Computer simulations have been telling us for several years that most of the 'missing' gas in the universe should be in hot filaments," said Smita Mathur, leader of the Ohio State team. "Most of those filaments are too faint to see, but it looks like we are finally finding their shadows."
NASA's Marshall Space Flight Center in Huntsville, Ala., manages the Chandra program, and TRW, Inc., Redondo Beach, Calif., is the prime contractor. The Smithsonian's Chandra X- ray Center controls science and flight operations from Cambridge, Mass.
Images and additional information about this result are available at:
http://chandra.harvard.edu
and
http://chandra.nasa.gov
I did not know that gravity was subject to remote detection, like X-Rays or Infrared.
Thanks ahead of time, Physicist.
I called upon Physicist because he has a real ability to explain these things to a poor barbaric SOB like me.
Maybe they should call it rivers of mass or matter instead, but what the astronomers are seeing is the effect of gravity from the mass. The dark matter in the universe forms a spongy structure similar to bone marrow. The "rivers" they are seeing is the connective fibers, which are so large from our perspective I guess it's appropriate to call them rivers.
There's a certain amount of deduction going on here. Theory (meaning computer simulations) tells them that there should be self-gravitating streams of hot gas between the galaxies.
You can get a taste of what these streams look like and how they form in a couple of simulations I ran using the National Scalable Cluster Project supercomputers here at Penn, using parallel code written by Prof. Paul Bode.
Since they expect the streams to be there, they set about to detect them by looking at the spectra of distant quasars. Since there are so many streams, they reasoned that some quasars must end up behind streams, from our point of view. In that case, the streams will block out part of the light from the obstructed quasars in a characteristic way in the x-ray band. This obstruction is what they have detected.
Note that this doesn't allow them to image the streams themselves; they just see the effect of the streams at a small number of points on the sky. They call them streams because that's what they expected to see. The same data might support the hypothesis that there are big gasseous blobs out there. But either way, the total mass of the gas can be estimated, and it is non-negligible.
It seems to all depend on what the programmer expects and programs for, not what may actually be detected.
Just like tomographs are only as good as the base data the programmer works with.
Have I confused everybody as bad as I confused myself ?
The point I'm trying to make is: How good is the interpetive data ?
Now there's a statement on our culture.
"Oooh! Oooh! Juicy tidbits about brutal death of some woman I've never met! Yeah...oh, darn. It's just a dumb post about the nature and origins of the universe. BOOOOORINNNNNG."
(Just a joke, no personal jab intended, no purchase necessary, batteries not included)
I count on you for no-BS facts.
If I fail to understand those facts, well that is my failing.
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