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Doing the pulsar twist.

Doing the pulsar twist

This "mystery spot,' the supernova's bright "companion,' also perplexes astronomers because they have a hard time figuring out what could produce it. Stirling Colgate of Los Alamos (N.M.) National Laboratory suggests what might have made the spot, which he calls "son of supernova.' It is part of his explanation of why a supernova explosion doesn't fall back on itself, and it involves the magnetic field of the pulsar that may form inside the supernova.

In 20 years of calculating how supernova explosions occur, Colgate says, he has always been puzzled by the question why the supernova explosion doesn't re-collapse. A supernova explosion begins with the collapse of the core of a massive star --one with 15 or 20 times the sun's mass. The sudden implosion of the core sends a shock wave outward that blows away the outer layers of the star.

But, says Colgate, as the shock proceeds it should meet discontinuities, boundaries between layers of different density. Eventually it should come to a layer 10 times its own density. That should reflect the shock, and the blow-back should cause much or all of the matter in the star's mantle to collapse back onto the core.

Observation, shows, however, that supernova explosions continue to expand. The only way to provide for this, Colgate says, is to use the magnetic energy of the collapsed core. With the proper amount of mass, the core collapses into a neutron star, and if it rotates and has the proper magnetic field, the neutron star will be a pulsar, producing radio waves, light or X-rays that terrestrial observers see in pulses. As the pulsar rotates, its magnetic field twists up into a helical shape that fills the cavity inside the exploding supernova front. That helical shape will exert a magnetic pressure that prevents the shock front from blowing back. Furthermore, as the shock front thins out with expansion, the magnetic pressure could pierce it at some point, sending out a stream of magnetic energy into space. The stream, by encountering and energizing some interstellar matter that happened to be in the neighborhood, he says, could produce the glowing "son of supernova.'
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Title Annotation:supernova explosions
Publication:Science News
Date:Oct 24, 1987
Words:362
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