Neutron star oscillations from starquakes

Abstract

Glitches are sudden increases in the otherwise extremely regular spin rate of pulsars. One theory proposed to account for these glitches is the starquake model, in which the spinup is caused by a sudden rearrangement of the neutron star crust. Starquakes can be expected to excite some of the oscillation modes of the neutron star. These oscillations are of interest as a source of gravitational waves, and may also modify the pulsar radio emission. In this thesis we develop a toy model of the starquake and calculate which modes of the star are excited. We start by making some order-of-magnitude upper estimates on the energy made available by the starquake and the amplitude of the modes excited, before moving on to a more detailed calculation based on a specific model of the starquake in which all strain is lost instantaneously from the star at the glitch. To find out which modes are excited by the starquake, we construct initial data describing the change in the star at the glitch, and then project this against the basis of normal modes of the star. We first carry out this procedure for a simplified model in which the star has spun down to zero angular velocity before the starquake. We find that the majority of the energy released goes into a mode similar to the fundamental mode of a fluid star. Finally, we describe the extension of this model to the more realistic case where the star is rotating before the glitch. We calculate the change in the normal modes of the star to first order in the rotation; these are no longer orthogonal, but we construct a scheme that still enables us to project our initial data against this set of modes, and discuss some preliminary results of the model