June 11, 2001 Astronomers from the University of Colorado at Boulder and the University of California at Berkeley have discovered a key building block for new stars in the rapidly expanding remains of an ancient stellar explosion.
Presented at the 197th meeting of the American Astronomical Society meeting June 3 to June 7 in Pasadena, Calif., the study provides insights into the early stages of a process by which violent stellar explosions help produce new stars.
"This finding is important because it gives us an example of how a supernova explosion can create new clouds of star-forming material," said Brian Rachford, a postdoctoral researcher at CU-Boulder's Center for Astrophysics and Space Astronomy.
Other participants in the study include Barry Welsh, a senior research scientist at UC-Berkeley's Space Sciences Laboratory and Jason Tumlinson, a doctoral student in CU-Boulder's astrophysical and planetary sciences department and a CASA research assistant.
The Monoceros Loop Supernova Remnant under study resulted from the cataclysmic explosion of a star nearly 100,000 years ago some 5,000 light-years from Earth, said Rachford. The supernova has formed a shell of gas 350 light-years across that is still expanding at a rate of 100,000 miles per hour.
One light-year -- the distance light travels through the universe in a year -- is equal to roughly 6 trillion miles.
The astronomers detected the presence of molecular hydrogen gas in the rapidly moving shell using a spectrograph onboard NASA's Far Ultraviolet Spectrographic Explorer, or FUSE, satellite. The spectrograph breaks up the ultraviolet light in a manner similar to the way a prism breaks up sunlight into a spectrum of individual colors.
The astronomers used a star located beyond the supernova remnant as a background light source. As the starlight passed through the gas, the molecular hydrogen imprinted a telltale signature on the spectrum, said Rachford.
The birth of new stars begins in cold, dark clouds of molecular hydrogen, which begin to form when individual hydrogen atoms join together in pairs.
"Astronomers have long suspected that supernova remnants can trigger the formation of new molecular clouds, but there had never been direct evidence of molecular hydrogen associated with such remnants before this discovery," he said.
FUSE allows access to the wavelengths of ultraviolet light where molecular hydrogen can be probed directly, said Welsh. Four FUSE telescopes collect and funnel UV light into a $9 million spectrograph designed and built by CU-Boulder’s CASA and which breaks down light like sunbeams passing through a prism.
"The observed molecular hydrogen appears to have formed while in the fast-moving supernova shell, but could represent previously existing cold gas that managed to survive the explosion," said Rachford.
Upcoming observations with FUSE will sample different portions of the Monoceros Loop Supernova Remnant to confirm the initial detection and look for additional, fast-moving molecular hydrogen.
The astronomers also plan to observe other supernovae in order to see if fast-moving molecular hydrogen gas clouds are a common feature in older exploded star remnants, said Welsh.
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