A starquake 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 starquakes to be the source of the giant gamma ray flares that are produced approximately once per decade from soft gamma repeaters. Starquakes are 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 spindown. As the neutron star loses angular momentum 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 they exceed a certain amount, the shape adjusts itself to a shape closer to 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 starquake was recorded on December 27, 2004, on the ultracompact stellar corpse (magnetar) SGR 1806-20. It released gamma rays equivalent to 1036 kW in intensity. This starquake 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.
Read more about this topic: Quake (natural Phenomenon)