Galaxies, Like People, Are Widely Diverse
Posted on: Friday, 9 January 2004, 06:00 CST
By PAUL RECER
ATLANTA (AP) -- A Hubble Space Telescope study designed to study evolution in the stellar universe has taken a mosaic of photos that includes more than 40,000 galaxies in a patch of sky about the size of the full moon.
The study, combining 78 separate exposures by the Hubble, gives astronomers a wide sampling of many galaxies that could be used to study how the massive groupings of stars originate, change shape and move together in clusters.
"Galaxies are just like people. There is a wide diversity," said Eric F. Bell of the Max Planck Institute for Astronomy in Heidelberg, a member of the astronomy team conducting the study.
Bell said the study suggests that there are at least 1.6 billion galaxies the size of the Milky Way, the sun's home galaxy, out to a distance of 9 billion light-years. A light-year is the distance light can travel in one year in a vacuum, about 5.8 trillion miles.
Only a fraction of the galaxies are bright enough to be closely studied. Most galaxies, such as the Milky Way, contain about 100 billion stars.
Bell said astronomers hope to learn how galaxies that formed alone tend to migrate and eventually form larger and larger groupings.
"Galaxies are gregarious - they like to clump and cluster," said Bell, speaking Thursday at the national meeting of the American Astronomical Society.
He said a simulation suggests that in about 7 billion years the Milky Way galaxy may merge with its nearest neighbor, the Andromeda, a large, bright galaxy about 2 million light-years away. When the two galaxies merge, it is expected they will form one large, elliptical galaxy.
The Milky Way is a spiral galaxy, a collection of stars with a black hole in the center and curving arms spreading out from the core. The solar system is on one of the spiral arms.
Bell said the majority of the galaxies within the study area of the Hubble mosaic are elliptical, probably the result of the merging of spiral galaxies during the last 9 billion years. He said these types of galaxies have about twice the stellar matter of galaxies that formed early in the history of the universe.
"This is exciting first evidence for a merger origin of at least some elliptical galaxies," he said.
Bell said astronomers still have an imperfect understanding of how galaxies form and change as they merge and form larger and larger groups.
By studying many galaxies across a wide swath of the sky, it will be possible to draw new conclusions about the history of galaxies, he said.
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