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Did supernovas pop top off galaxy?

Did supernovas pop top off galaxy?

For decades, scientists have wondered what could make the unusual galaxy m82 look so spectacular. Its polar caps seem to be blown off, and hot filaments of gas stream forth from those regions. In 1963, astronomers proposed that a giant explosion in the center of the galaxy caused the unusual formation. However, there are no good proposals for how such an explosion would take place, according to R. Brent Tully of the University of Hawaii's Institute for Astronomy in Honolulu.

Tully and colleague Jonathan Bland propose a somewhat different history for the galaxy in the July 7 NATURE. They suggest galactic gas was blown off not by a huge explosion of a type previously unknown, but rather by many smaller explosions of the more familiar supernova type.

Part of the evidence they cite for this is that the gas coming out of the galaxy keeps accelerating as it gets farther from the galactic center -- something that would happen only if explosive activity is still going on and pushing at the gas as it leaves.

M82 may contain many more supernovas than usual because the galaxy recently (in astronomical terms) had a close encounter with the nearby galaxy M81, which probably stirred up M82 and lead to a burst of star formation, Tully says. Many of the larger stars formed would pass quickly through their life cycles and become supernovas, he adds.

At first, the supernovas "blew off the caps" of the galaxy; later explosions have created a "galactic wind" that keeps blowing gas out of the galaxy, Tully says. As additional evidence for this, he and Bland point out that radiotelescopes have spotted more supernova remnants in M82's galactic center than might be expected.

The new theoy has wider significance. Supernova activity has long been proposed as the mechanism for keeping elliptical galaxies free of interstellar gas, but such a mechanism has been "rather speculative," Tully says. Although M82 is not an elliptical galaxy, it makes a good cause for such a mechanism, he says.
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Title Annotation:galaxy M82
Publication:Science News
Date:Jul 30, 1988
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