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HIDDEN SUPERNOVA REVEALS DUST-ENSHROUDED "SUPERNOVA FACTORY"
An exploding star (supernova) veiled by dust in a colliding galaxy is apparently part of a "supernova factory," a region where stars are exploding at a furious rate 50 times greater than in an entire galaxy. The supernova factory is a cosmic version of a "living fossil," providing insight into how stars were born billions of years ago in the early Universe.
Using the National Science Foundation's Very Long Baseline Array (VLBA) radio telescope, astronomers discovered the newly-exploded star hidden deep in a dust-enshrouded supernova factory in a galaxy some 140 million light-years from Earth. The dust blocked visible light from the new supernova and others in the factory, preventing astronomers from seeing them with optical telescopes. However, radio emission from the supernovae passed through the dust, granting a glimpse to astronomers using radio telescopes.
"This supernova is likely to be part of a group of super star clusters that produce an average of one such stellar explosion every two years," said Dr. James Ulvestad, of the National Radio Astronomy Observatory (NRAO) in Socorro, NM. "We're extremely excited by the tremendous insights into star formation and the early Universe that we may gain by observing this 'supernova factory,'" he added.
Ulvestad worked with Dr. Susan Neff of NASA's Goddard Space Flight Center in Greenbelt, Md., and Stacy Teng, a graduate student at the University of Maryland, on the project. The scientists presented their findings at the American Astronomical Society's meeting in Nashville, TN.
Supernovae shine fiercely -- as brilliant as 100 billion suns. They occur when the core of a massive star exhausts its fuel and collapses under its own gravity, generating a shock wave that blasts the star's outer layers into space. This ejected material, called a supernova remnant, contains heavy elements, including those essential to life, that are later incorporated into new generations of stars and planets.
"These super star clusters likely are forming in much the same way that globular clusters formed in the early Universe, and thus provide us with a unique opportunity to learn about how some of the first stars formed billions of years ago," Neff said.
The cluster is in an object called Arp 299, a pair of colliding galaxies, where regions of vigorous star formation have been found in past observations. Since 1990, four other supernova explosions have been seen optically in Arp 299.
Observations with the NSF's Very Large Array (VLA) earlier showed a region near the nucleus of one of the colliding galaxies which had all the earmarks of prolific star formation. The astronomers focused on this region, prosaically dubbed "Source A," with the VLBA and the NSF's Robert C. Byrd Green Bank Telescope in 2002, and found four objects in this dusty cloud that are likely young supernova remnants. When they observed the region again in February 2003, there was a new, fifth, object located only 7 light-years from one of the previously detected objects. More observations on April 30 - May 1, 2003, showed that this new object has typical characteristics of a supernova explosion by a young, massive star.
"This supernova is exploding in a very dense environment, quite different from the environments of supernova explosions that can be seen in visible light," Teng said. "This is the kind of dense environment in which stars likely formed in the early Universe," she added.
The astronomers believe the super star cluster in Arp 299 saw its most recent peak of star formation some 6 - 8 million years ago, and now its massive stars, 10 - 20 times (or more) as massive as the Sun, are ending their lives in supernova explosions. Super star clusters typically contain up to a million stars, which is why the scientists think Source A will see frequent supernova explosions. "We plan to keep watching this region, and hope that we can study numerous supernovae, and gain important new information about the processes of star formation, both in the early Universe and at the present time," Neff said.
"Because of the dust and the distance, only a radio telescope with the VLBA's ability to see fine detail can find the supernovae in this region," Ulvestad said.
The VLBA is a continent-wide system of ten radio-telescope antennas, ranging from Hawaii in the west to the U.S. Virgin Islands in the east, providing the greatest resolving power, or ability to see fine detail, in astronomy. Dedicated in 1993, the VLBA is operated from the NRAO's Array Operations Center in Socorro, New Mexico. The National Radio Astronomy Observatory is a facility of the National Science Foundation, operated under cooperative agreement by Associated Universities, Inc.
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