1E 0657-56: NASA Finds Direct Proof of Dark Matter

Dark matter and normal matter have been wrenched apart by the tremendous collision of two large clusters of galaxies. The discovery, using NASA's Chandra X-ray Observatory and other telescopes, gives direct evidence for the existence of dark matter.

http://chandra.harvard.edu/photo/2006/1e0657/

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Chandra Chronicles: Bedeviling Devil's Advocate Cosmology

In the last decade incredible progress has been made in finding answers to some of the most exciting questions in astronomy such as: what is the universe made of, how big is it, how did it begin and what is its future? Astronomers have also converged on a cosmology where "normal" matter, the material found in our bodies, the Earth and the stars makes up only a few percent of the universe. And, a vast majority of scientists agree that most of the matter in the universe is invisible - dark matter - and consists of some kind of exotic particle that is yet to be discovered.

http://chandra.harvard.edu/chronicle/