Slide 14 of 59
Notes:
Glitches are believed to be caused by ‘starquakes’, analogous to earthquakes, as the crust of the star establishes a new equilibrium with respect to the superfluid interior.
This model works for the Crab pulsar, but not for the Vela pulsar because the glitches occur too frequently.
An alternative model for the glitches is the catastrophic unpinning of vortices in the rotating neutron superfluid. These vortices exist because, on a macroscopic scale, a rotating superfluid must rotate irrotationally. Thus a superfluid is made up of an array of vortices whose axes lie parallel to the rotation axis. The vortices are either pinned to nuclei in the crust or thread the spaces between them. As the star slows down and angular momentum is transferred outwards, the vortices migrate. This is a jerky, not smooth process and causes small glitches. The giant glitches are believed to be caused when the vortices are unpinned catastrophically and a change in the rotational speed results.