Violent Starquakes

A neutron star is the dense core left behind when a massive star explodes as a supernova. Some have such powerful magnetic fields that they rip themselves open due to magnetic forces.


The spins of some neutron stars decrease rapidly, and extremely powerful magnetic fields that radiate electromagnetic energy may slow their rotation. This type of neutron star is called a magnetar.

New observations of a candidate magnetar have confirmed that it has a magnetic field 600 trillion times the strength of Earth's field – powerful enough to explain the 'starquake' it experienced in 2003.

Researchers used the XMM-Newton spacecraft to measure X-rays from a neutron star called XTE J1810-197, which lies about 10,000 light years from Earth in the constellation Sagittarius.

Discovered in 2003 when it had a major outburst, suddenly becoming more than 100 times brighter than normal in X-rays. The event was similar to magnetic starquakes seen on other candidate magnetars.

The idea is that the crust of the neutron star buckles and cracks due to the magnetic forces exerted by the star's own magnetic field.
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There were other possible explanations of these outbursts, such as sudden changes to the magnetosphere (cloud of charged particles) that surrounds the stars.

By analysing the spectrum of X-rays coming from XTE J1810-197 since its 2003 outburst, the research team determined the existence of a hot spot about 7 kilometres wide at the neutron star's surface. The spot was heated to about 5 million degrees by the outburst, and has been cooling since then. This is consistent with the starquake theory, in which the part of the neutron star's crust that buckles releases tremendous energy and heats up its surroundings.

Jules Halpern of Columbia University in New York City, US, says further studies of such outbursts may reveal why magnetars have such short lives. The known magnetars all appear to be very young – most are less than 10,000 years old.

It may be the case that hundreds of outbursts over the lifetime of the star are responsible for dissipating most of the magnetic field. After that . . . they may turn into ordinary radio pulsars or some other type of neutron star.

Reference: The Astrophysical Journal Letters (vol 667, p 73)
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