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Hydrogen clouds colder than expected.

Hydrogen clouds colder than expected

Analyzing the absorption of quasar light passing through hydrogen clouds near the edge of the observable universe, astronomers have found indications that some of these clouds are about 20,000 kelvins colder than previously thought.

Using a high-resolution, wide-area spectrograph, Linda Smith of University College London in England and her colleagues studied absorption lines in the spectra of quasar light that older instruments had rendered too blurry to analyze. They found that the lines were narrower than believed, indicating that the hydrogen clouds had temperatures of 5,000 to 10,000 kelvins, well below the expected 30,000.

Smith notes the finding has several implications for the evolution of the clouds, which astronomers believe do not contain enough hydrogen to form galaxies. If the clouds maintain thermodynamic equilibrium with their surroundings at the lower temperature inferred from the new data, the material must concentrate in thin sheet, Smith says. A competing theory holds that the clouds possess the standard spherical shape but continue to expand and cool rather than maintain equilibrium.

She notes that recent calculations by other researchers support the expansion notion. Smith and co-workers in Australia at the University of Sydney and the Anglo-Australian Observatory in New South Wales report their findings in the Oct. 15 MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY.
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Title Annotation:in space
Publication:Science News
Date:Oct 20, 1990
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