Discovery Of Supernova Remnants May Shed Light On Birth Of Stars

February 11, 1997

CHAMPAIGN, Ill. -- New observations reveal that a previously known supernova remnant in the Large Magellanic Cloud is, in fact, two colliding supernova remnants, a team of researchers from the University of Illinois reports.

"Images taken with both optical and radio telescopes show the object, designated DEM L 316, to consist of two overlapping shells, while X-ray observations show an area of shock-heating where the shells intersect," said Rosa Murphy Williams, a graduate student in astronomy at the U. of I. "This is the first time we've been able to demonstrate that two remnants are colliding."

By studying this collision, said You-Hua Chu, a U. of I. professor of astronomy, "We hope to gain a better understanding of how the energy and heavy elements produced by supernovae are distributed out to the galaxy at large by the remnants. Since the next generation of stars will form out of this material, we're actually examining how the deaths of old stars influence the births of new ones."

When a massive star nears the end of its life, the outward pressure of its thermonuclear reactions can no longer counter the inward pull of gravity, Williams said. "The star collapses in on itself and, within a fraction of a second, rebounds in a tremendous explosion called a supernova. Much of the star's material is flung outward, forming an expanding sphere of gas and dust called a supernova remnant, which sweeps up large quantities of interstellar material as it expands. These remnants are the means by which energy and heavy elements produced by supernovae are distributed through interstellar space."

The colliding supernova remnants are in the Large Magellanic Cloud, a small neighboring galaxy to our own Milky Way, about 160,000 light-years from earth.

In the past, some astronomers assumed these strange objects were two supernova remnants that merely happen to lie along the same line of sight. Other astronomers suggested that DEM L 316 was a single remnant whose unusual shape was due to its surroundings.

However, new X-ray observations of the million-degree gas that forms behind the shock wave of a rapidly expanding supernova remnant show two separate regions of X-ray emission within the shells and a significant X-ray brightening near the juncture between them, Williams said.

In addition, optical observations of the velocity and structure of the much cooler dense gas in the shells show highly disturbed material indicative of an interaction, and radio observations show a "twisting" and compression of the magnetic field between the two shells. All of these factors led the researchers to conclude that the two shells are indeed colliding supernova remnants.

In addition to Williams and Chu, the research team included John R. Dickel and Ross Beyer of the U. of I., Robert Petre of the Goddard Space Flight Center, R. Chris Smith of the University of Michigan and D.K. Milne of the Australian Telescope National Facility. The team's findings will appear in the May 10 issue of the Astrophysical Journal.

University of Illinois at Urbana-Champaign

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