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SCIENCE / ASTRONOMY : More Light Is Shed on Universe's Dark Matter

August 11, 1994| From Times Wire and Staff Reports

A group of U.S. astronomers has reported finding what could be dark matter, a key missing component of the universe, in a distant galaxy. The find appears to bolster a similar discovery reported last year.

Scientists have been searching for years for evidence that dark matter exists. According to what is known about the universe, ordinary visible matter--stars, gas, dust and planets--do not have sufficient mass by themselves to cause gas to condense into stars, stars to clump into galaxies and galaxies to gather into clusters.

The missing mass, they theorize, must be accounted for by dark matter, either in the form of massive halo objects--also known as brown dwarfs--or as exotic forms of subatomic matter.

Penny Sackett of the Institute for Advanced Study in Princeton, N.J., said an examination of a distant spiral galaxy found strong evidence of the elusive dark matter.

"While searching for faint starlight away from the plane of the edge-on spiral galaxy NGC5907, we have found that the galaxy is surrounded by a faint luminous halo," she wrote in today's issue of the science journal Nature.

"The intensity of light from this halo falls less steeply than any known luminous component of spiral galaxies, but is consistent with the distribution of dark mass inferred from the galaxy's rotation curve."

In other words, the galaxy acts as if it contains more matter than can be accounted for by standard measurements.

The report said the faint light could be coming from small bodies such as dark, shrunken suns, made up of dark matter. "Could the faint halo light of NGC5907 be composed of dim, low-mass stars that not only trace the dark matter, but are also responsible for all of its dark mass?" it asked.

Theoretical astrophysicists believe that visible matter may account for only 0.1% to 10% of the universe. Last fall, researchers from the United States, Australia and France reported that three stars in the nearby Large Magellanic Cloud briefly grew brighter than usual, almost certainly because gravity from dark matter bent the star's light rays into focus on Earth. This, they said at the time, appeared to be the first direct evidence of the existence of dark matter.

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