Hubble camera finds huge star clusters.

They could be the Arnold Schwarzeneggers of star clusters. When the Hubble Space Telescope peered into the center of an oddly shaped galaxy called Arp 220, it imaged six densely packed clusters of stars -- the largest star-packed regions ever observed by a telescope.

Ten times larger and thousands of times more luminous than the elderly, densely star-packed regions that surround our Milky Way, bigger and brighter than the young, giant clusters that Hubble found in the elliptical galaxy NGC 1275 (SN: 4/6/91, p.218; 1/25/92, p.52), the youthful star clusters in Arp 220 likely emerged after a violent collision, report Edward Shaya and Dan Dowling of the University of Maryland in College Park. The researchers suspect that two spiral galaxies collied to form Arp 220; star clusters could arise from the dust and gas unleashed in such a merger.

In 1983, NASA's Infrared Astronomy Satellite revealed that Arp 220 is one of the brightest of about a dozen galaxies that emit most of their light in the infrared. Since then, scientists have debated the source of the brightness. Shaya, who presented the new findings this week at a press briefing in Washington, D.C., says it now appears that the newly discovered star clusters account for about half the galaxy's luminosity, with the rest coming from a compact source that Hubble has seen at the center of the galaxy. He estimates that the clusters are about 20 million years old, radiate a billiontimes the total energy output of the sun and contain many massive, short-lived stars that may soon explode as supernovas. The giant clusters may last only a few hundred million more years before tidal forces at the galaxy's center rip them apart.