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Molecular gas in the Milky Way.

For the first time, researchers have detected molecular gas at the extreme fringes of the Milky Way. Using a millimeter-wave radio telescope mounted on the roof of a campus building, Seth W. Digel and Patrick Thaddeus of the Harvard-Smithsonian Center for Astrophysics in Cambridge, Mass., found that clouds of carbon monoxide -- a tracer of molecular hydrogen gas -- extend along the outskirts of the disk-shaped Milky Way, 100,000 light-years from the galaxy's center. Surveying the galaxy with the same instrument, Thaddeus and Harvard-Smithsonian colleague Thomas M. Dame found that carbon monoxide also extends 1,000 light-years above and below our galaxy's thin disk.

Although astronomers knew that sheets and filaments of atomic hydrogen reach as high as 3,000 light-years above the Milky Way, it appeared that molecular gas extended no higher than 350 light-years. Dame speculates that the higher-altitude gas he discovered originated in the disk and was pushed upward by stellar winds or supernova explosions.

The molecular clouds found by Digel and Thaddeus at the outskirts of the Milky Way have about the same width and mass as those near the sun. But the outlying clouds appear much fainter in light emitted by carbon monoxide, suggesting that they are cold and do not form massive stars. Digel says he plans to investigate whether the molecular clouds have too low a density to make stars or whether some unknown process prevents starbirth there.
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Author:Cowen, Ron
Publication:Science News
Article Type:Brief Article
Date:Jul 4, 1992
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