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STUDY CHALLENGES THEORY ABOUT DARK MATTER

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A study of small galaxies challenges a popular idea for what constitutes most of the matter in the universe.

Scientists know the universe contains more matter than they can see. In fact, so-called missing or dark matter may make up 90 percent or so of the matter in the universe.Nobody knows what this stuff is, but one popular candidate is "cold dark matter," a class of exotic, hypothesized particles that have never been seen.

That theory is challenged in the study by Ben Moore, a research associate in the astronomy department at the University of Washington in Seattle.

Moore took advantage of the theoretical prediction that cold dark matter would surround galaxies in huge, invisible haloes and affect the galaxies' rotation in a predictable way. Using observations by other scientists of four small "dwarf" galaxies, he found that the inner parts of the galaxies were rotating much more slowly than one would expect if their haloes were made of cold dark matter.

"This challenges the basis of the whole cold dark matter theory," Moore said in a telephone interview.