By Ron Cowen
Viewing galaxies so distant that the light now reaching Earth reveals what they looked like billions of years ago isn’t the only way to learn about how galaxies form. Astronomers can examine a much closer specimen–our own Milky Way.
In contrast to previous Milky Way projects, which measured the motions of some 2.5 million stars as they march across the sky, a survey that began in April will track the movement of stars toward or away from Earth. By measuring this component of motion, which is currently known for only 20,000 stars, astronomers plan to reconstruct more details about how the Milky Way formed.
The survey, known as RAVE (Radial Velocity Experiment), uses a 1.2-meter telescope in Coonabarabran, Australia. By 2005, scientists expect RAVE to have measured the radial motion of 100,000 stars. With these data, astronomers will identify dozens, perhaps hundreds, of star groupings that appear to be streaming coherently, says RAVE leader Matthias Steinmetz of the Astrophysical Institute in Potsdam, Germany.
Since these streams represent the remnants of small satellite galaxies that were snared by the Milky Way billions of years ago, they’ll indicate how the galaxy’s components assembled.
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