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Supernova mystery: cracking the Crab.

Supernova mystery: Cracking the Crab

The crab Nebula, a patch of glowing gas representing the debris from a stellar explosion bright enough for Chinese scholars to record nearly 1,000 years ago, has long been the target of telescopes and astronomical investigations. However, despite its well-documented start and much subsequent study, a great deal remains to be learned. Recent studies indicate the nebula has an unusual distribution of chemical elements and a surprisingly complex structure, including gigantic bubbles within its envelope of expanding gas. Such findings may force a revision of theories concerning what happens during a supernova explosion.

"The Crab Nebula is one of the most studied but least understood objects in our galaxy," says astronomer Gordon M. MacAlpine of the University of Michigan in Ann Arbor, who has been investigating the nebula's composition. He and his co-workers described their most recent results at least week's American Astronomical Society meeting in Ann Arbor.

Several of the Crab Nebula's unusual features show up in a color-coded image comparing the amount of light emitted by hydrogen and helium atoms in the cloud. A white strip (see illustration), several light-years across, appears to be a ring of nearly pure helium gas encircling the spinning neutron star, or pulsar, at the nebula's center. Huge, rapidly expanding, bubble-like structures lie above and below this ring. In the dark-blue region near the picture's top, the nebula's gas seems to have jammed itself up against a molecular cloud. This region has an unusually high concentration of nickel.

A new estimate of the amount of gas in the nebula suggests the supernova star that produced the nebula was at least twice as massive as astronomers had thought. MacAlpine's calculations put the star's mass at 20 to 30 times that of the sun.
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Title Annotation:Crab Nebula
Author:Peterson, I.
Publication:Science News
Date:Jun 24, 1989
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