Star-quakes – Pulsars and Quasars

A star-quake is an astrophysical phenomenon that occurs when the crust of a neutron star undergoes a sudden adjustment, analogous to an earthquake on Earth. A paper published in 2003 in Scientific American by Kouveliotou, Duncan & Thompson suggests these star-quakes to be the source of the giant gamma ray flares that are produced approximately once per decade from soft gamma repeaters.
Star-quakesare thought to result from two different mechanisms. One is the huge stresses exerted on the surface of the neutron star produced by twists in the ultra-strong interior magnetic fields. A second cause is a result of spin-down. As the neutron star loses angular velocity due to frame-dragging and by the bleeding off of energy due to it being a rotating magnetic dipole, the crust develops an enormous amount of stress. Once that exceeds a certain amount, the shape adjusts itself to a shape closer to non-rotating equilibrium: a perfect sphere. The actual change is believed to be on the order of micrometers or less, and occurs in less than a millionth of a second.
The largest recorded star-quake was recorded on December 27, 2004, on the ultra-compact stellar corpse (magnetar) SGR 1806-20. It released gamma rays equivalent to 1036 kW in intensity. This star-quake occurred 50,000 light years away. Had the event occurred within a distance of ten light years from Earth, the event could have potentially triggered a mass extinction on Earth.

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