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Hubble Images Show Multiple-Galaxy Collisions
By Kenneth Silber
Staff Writer
posted: 05:54 am ET
22 November 1999
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hubble_galaxiesNewly released images from the Hubble Space Telescope show multiple galaxies -- sometimes as many as five at a time -- colliding to form bright galaxies called ULIRGs (ultra-luminous infrared galaxies). Astronomers led by Kirk Borne of NASA's Goddard Space Flight Center used the orbiting telescope to conduct a three-year survey of 123 ULIRGs, which are between 100 and 1,000 times brighter than the Milky Way. While it has been thought that such brightness results from galactic collisions, which increase the rate of star formation, it has not been clear until now that such collisions often involve more than a pair of galaxies. The survey found that at least 20 percent of ULIRGs result from multiple-galaxy collisions. 
The survey covered ULIRGs that are, as Borne puts it, "nearby" -- between 700 million and 3 billion light-years from Earth. However, he notes, such objects are more common in distant parts of the universe, up to 10 billion light-years away, from which light has taken a long time to travel. Thus, he says, these images (although they are of comparatively recent events) provide a "relic of the past," since multiple-galaxy collisions were more common in the early universe.
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