Hubble finds cluster of exploding stars

Data to shed light on universe's origin

NASA's Hubble Space Telescope has discovered a potentially rich source of massive, young, exploding stars for astronomers to study, lending support to an emerging theory of galaxy formation, scientists said Tuesday.

The findings associated with ARP 220, a high-energy galaxy 220 million light-years away, may also account for some of the celestial violence once attributed solely to mysterious black holes.

One of the most energetic objects yet observed, the distant galaxy is 1 trillion times brighter than the sun.

"We've never had a really great view of star bursts of these dimensions before," said Steve Marin, a Hubble astronomer at NASA's Goddard Space Flight Center in Greenbelt, Md.

Scientists say ARP 220, one of a recently discovered class of objects known as ultraluminous infrared galaxies, may spawn one supernova or exploding star per month.

Astronomers worldwide celebrated in early 1987 when they spotted a rare supernova 50 million light-years away in the constellation Virgo, their first observation of a stellar explosion since the early 17th century.

ARP 220 was discovered in 1983 by another orbiting observatory, NASA's Infrared Astronomy Satellite, which noted an unusually high level of energy produced in an invisible region of the electromagnetic spectrum. Subsequent observation suggested that the object was produced by two colliding galaxies composed of dust and gas.

The work piqued the interest of Hubble astronomers who are using the orbiting telescope to study the birth and expansion of the universe.

According to University of Maryland astronomer Edward Shaya, the Hubble studies may shed light on the formation of stars and galaxies.

Obscured deep within ARP 220, a powerful source for about half the total energy coming from the object was observed by Hubble astronomers.

The phenomenon typically is associated with the presence of a massive black hole residing within the center of brilliant young galaxies.

Surrounding that source, Shaya has counted a half-dozen bright clusters of massive stars that account for the other half of the object's tremendous energy output.

"What we are beginning to realize is that in young galaxies where there is violent optical phenomena going on, it may not necessarily be that giant black holes are responsible for this high outburst of energy," said Bruce Margon, a University of Washington astronomer. "It may be stellar births."

If the theory is correct, stars may form when clouds of stellar dust and gas collide.

Then, drawn by gravity, small galaxies may collide to form ever larger galaxies, an evolutionary process still at work in our corner of the 10-billion to 20-billion-year-old universe.

According to Shaya, the Milky Way will likely experience a near miss with Andromeda, its galactic twin, which spirals a million light-years away, in 5 billion to 10 billion years.