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An international research team has found that massive clouds of gas appear to play a key role in the ability of the Milky Way to produce new stars. The 10-member team, which includes an astrophysicist from Lewis & Clark College, reports in the current issue of the journal Nature that the massive clouds rain gas down onto Earth's home galaxy, seeding it with star-forming material. Data from the Hubble Space Telescope and five other telescopes were used to evaluate what astronomers call high-velocity clouds, mysterious structures that move through space at high speeds and do not rotate along with the rest of the Milky Way. These clouds--discovered 35 years ago--move at about 225,000 to 450,000 mph far above the galaxy's rotating disk. Stephen L. Tufte, assistant professor of physics at Lewis & Clark, used the Wisconsin H-Alpha Mapper, or Wham, at Kitt Peak National Observatory near Tucson, Ariz., to explore the ionized hydrogen and other faint material in the distant clouds. Viewed edge-on, the Milky Way appears similar to a flying saucer, with a slight central bulge tapering off into a disk called the galactic plane. Above this plane of roughly 100 billion stars is the Milky Way's "halo," which has much lower concentrations of stars and other material. The evidence from the new study reveals an inventory of some of the heavy elements in a high-velocity cloud that lies between 10,000 and 40,000 light years above the galaxy's plane in the halo area. A light-year is how far light travels in one year, nearly 6 trillion miles. Every star in the Milky Way was born of gas millions or billions of years ago, and the stars continually turn hydrogen into helium or heavier elements, such as metals. They shed these metals back into interstellar space. The study's findings show that some of the high-velocity clouds are raining metal-poor gas into the galaxy, offsetting the metal production by stars in the Milky Way disk. "Our results show that the material is coming into the galaxy for the first time," Tufte said. "If the material came from the plane of the Milky Way, you would expect it to have a significant quantity of elements heavier than helium, because when stars form they create these heavier elements, then spit them back into interstellar space. What we found is that the material is fairly pristine--it doesn't have much of the heavier elements, so it couldn't have been a part of the Milky Way."
A Lewis & Clark professor contributes to the study of the mysterious structures above the Milky Way. The study supports a theory that there is a continual flow of material into the galaxy to account for the continuing formation of stars. The research also explains how the Milky Way can produce a new star each year, on average, without running out of its supply of gas. Other researchers in the study were from the University of Wisconsin at Madison, Johns Hopkins University, and universities and institutes in the Netherlands, Germany and Great Britain. Tufte received his doctorate from the University of Wisconsin at Madison, where he helped to develop Wham. He is setting up a remote observing laboratory at Lewis & Clark that will allow his students to operate Wham at Kitt Peak this summer via the Internet. "I'm excited about having students participate in my investigations of high-velocity clouds," he said. "They will be able to learn firsthand about how to obtain and analyze data in exploring the universe." - by Richard L. Hill Wednesday, December 1, 1999, The
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