Glitch (astronomy)

In the context of astronomy, a "glitch" refers to a sudden, unpredictable, and relatively small change in the rotation rate of a neutron star, particularly a pulsar. These events are distinct from the gradual spin-down that these stars experience due to the emission of electromagnetic radiation and particle winds, which steadily reduces their rotational speed.

Glitches are characterized by an abrupt increase in the pulsar's rotation frequency (spin-up), followed by a gradual relaxation back towards its pre-glitch spin-down rate. The amplitude of these glitches is typically very small, often on the order of parts per million or even less, but the suddenness and nature of the change make them a significant phenomenon for study.

The underlying mechanisms responsible for glitches are not fully understood, but the most widely accepted explanation involves the interaction between the superfluid interior and the solid crust of the neutron star. In this model, the neutron star's interior is believed to contain a superfluid composed primarily of neutrons. This superfluid rotates without friction and is not directly coupled to the crust, which is composed of ordinary matter. As the pulsar spins down, the superfluid rotates faster than the crust. At some point, the difference in angular velocity becomes too great, and the superfluid releases some of its angular momentum to the crust in a sudden event, causing the observed spin-up.

The relaxation period after the initial spin-up is thought to be due to the gradual recoupling of the superfluid and the crust, allowing the angular momentum transferred during the glitch to be redistributed and dissipated.

The study of glitches provides valuable insights into the internal structure and dynamics of neutron stars, helping astronomers probe the extreme physics occurring within these dense stellar remnants. The frequency and size of glitches can provide information about the properties of the superfluid, the strength of the coupling between the superfluid and the crust, and the overall evolution of the neutron star.