Neutron starquakes
One way to figure out what neutron stars are made of is made of is to study their seismic vibrations. This is the approach that is used by geologists and geophysicists, for example, to figure out the interior structure of the Earth. Studying the effect of starquakes on neutron stars if of course rather harder (since we can't go and place a seismometer on the star's surface!) but the telltale signs of starquakes can be seen by studying the electromagnetic radiation emitted by the star. We are studying starquakes on a particular class of neutron stars called magnetars, which have very strong magnetic fields. These strong fields get tangled up and reconnect, launching strong gamma-ray flares, in a process similar to that which launches solar flares. As the magnetic field lines twist and snap they can set the star vibrating. By studying the frequencies of the vibrations excited by the flares, we can figure out the properties of the star's interior - such as the thickness of the star's solid crust. This tells us how matter behaves when it is crushed to extreme pressures.
Fig. 1: A neutron star that has been been set into vibration by a starquake (Image credit: Anna Watts)
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