This word, until now not often seen outside the specialist field of cosmology, has suddenly became a hot topic. Reports have recently appeared of a colossal burst of gamma rays which hit the Earth’s upper atmosphere on 27 August 1998. The pulse lasted about five minutes, ionised the atmosphere on the night side to levels normally seen in daytime, disrupted some radio traffic, sent detectors on several spacecraft off scale and caused one to shut down completely.
What is astonishing about this phenomenon is that it was traced to a star some 20,000 light years away, of a strange and rare kind known as a magnetar. Astronomers think they are young neutron stars, formed in supernova explosions, which are rotating at speeds that approach a thousand times a second. This rotation generates immense magnetic fields. The heat generated by the movement of the field through the iron crust of the neutron star quickly becomes so great that it cracks apart in what has been dubbed a starquake, the stellar equivalent of an earthquake. This causes the release of vast amounts of gamma rays. Though our atmosphere protects us from the radiation, such huge bursts can, as we’ve seen, knock out satellites.
The name is a blend of magnetic and star; it was coined by Robert Duncan and Christopher Thompson in a paper in the Astrophysical Journal in 1992; these exotic stars are also called soft gamma repeaters, a name which was given to them after a huge radiation burst was observed in 1979 and long before their true nature was realised.
“In ordinary neutron stars the crust is stable, but in magnetars, the crust is stressed by unbearable forces as the colossal magnetic field drifts through it,” said Duncan.
Space Science News, May 1998
A young magnetar would be very hot, because of frictional heat generated by mobile material, redistributed by the powerful magnetic field.
New Scientist, Aug. 1998
Page created 10 Oct. 1998
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