In astronomy, a glitch is a sudden small increase of around 1 part in 1 million in the rotational frequency of a pulsar, which usually decreases steadily due to braking provided by the emission of radiation and high-energy particles.
As of 2024[update] only multiple glitches of the Crab and Vela pulsars have been observed and studied extensively.
This differs from the steady decrease in the pulsar's rotational frequency, which is caused by external processes.
This brief coupling transfers angular momentum from core to surface, which causes a decrease in the measured period.
More generally, observations of pulsar glitches allow indirect information on the dense nuclear matter in neutron star interiors to be inferred, in particular its superfluid properties.