Re: Cosmic structure explained without dark matter?
- From: Sam Wormley <swormley1@xxxxxxxxx>
- Date: Fri, 29 Dec 2006 01:12:30 GMT
G=EMC^2 Glazier wrote:
Sam Posted that dark matter an transparent matter are relative.
No, Herb, what I posted was:
The scientists making the observations, are convinced they have
definitive evidence for the existence of dark matter. Next up
will be the discovery of what is consists of.
Dark Matter Exposed?
http://sciencenow.sciencemag.org/cgi/content/full/2006/821/1
By Tom Siegfried
ScienceNOW Daily News
21 August 2006
A smoking bullet clinches the case for dark matter in galactic
clusters, NASA announced today. The cluster of galaxies designated
1E0657-56, known as the "bullet cluster" for its picturesque
bullet-shaped cloud of superhot gas, has provided astronomers with the
best evidence yet that intergalactic space is filled with the same
stuff that provides the gravity needed to hold the galaxies together.
Normal matter in galactic clusters consists mostly of stars and very
hot gas-- the gas between the galaxies, in fact, outweighs all the
stars. But the gas and stars together appear to be vastly outweighed
themselves by some mysterious form of unseen matter, composed of an as
yet unidentified species of particle (ScienceNOW, 7 February)
Previously, dark matter's existence had been inferred from its
gravitational effects on the motions of galaxies. But some scientists
suspected that odd galactic motions could be explained without the need
for dark matter if gravity's strength was merely altered on galactic
scales.
But such "modified" theories of gravity can't explain away the new
observations, report astronomer Douglas Clowe of the University of
Arizona in Tucson and colleagues. Images from NASA's Chandra X-ray
satellite indicate that the bullet cloud was formed by an explosive
collision between galactic clusters, with the shock wave dragging the
hot gas between the galaxies into its peculiar shape. The shock wave
would not have affected dark matter, which interacts only via gravity,
so the collision effectively separated the dark matter from the gas.
Images from the Hubble Space Telescope and other telescopes show that
the strength of the cluster's gravity no longer matches up with the hot
gas, indicating that a stronger gravitational source--the dark
matter--exists in the cluster. Those images show how the cluster's
gravity bends light and distorts the images of distant background
galaxies.
"For the first time, we're actually able to see dark and ordinary
matter separated in space. And this proves in a simple and direct way
that dark matter exists," said astrophysicist Maxim Markevitch, of the
Harvard-Smithsonian Center for Astrophysics, in Cambridge,
Massachusetts, at a NASA briefing. Markevitch is a member of the team
led by Clowe that will present its findings in an upcoming issue of
Astrophysical Journal Letters.
The data make the case "beyond a reasonable doubt" that galactic
clusters are held together by dark matter rather than a modified
gravity, says University of Chicago cosmologist Sean Carroll. "Evidence
[for dark matter] has been accumulating for a long time," Carroll says,
"and the great thing about this particular result is there are
pictures."
.
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