When Stars Glitch

Every armchair astronomer is familiar with the concept of violently rotating neutron stars, better known as pulsars. They are, after all, popular celestial objects with unique characteristics. For instance, pulsars are highly magnetized and accompanied by beams of radiation emanating from their magnetic poles. Pulsars have regular periods that causes them to pulse in precise intervals. This pulsing is, in fact, so regular that certain types even rival atomic clocks in terms of their time keeping precision. These facts are well known to a general consumer of popular science. What may be lesser known, however, is that they sometimes glitch.

Occasionally, pulsars have been known to exhibit a sudden, usually temporary change in rotational frequency. This event has been dubbed a glitch. Glitches can be as large as one millionth the usual rotational frequency. Small, but not too small to notice.

After a glitch has been detected, the pulsars typically return to their normal rotational frequency during a finite recovery period. Recovery periods can range from days to years. Though the exact reasons for the glitch can only be speculated at this time, the leading idea is that the pulsar's typically faster rotating internal fluid briefly matches the rotational frequency of the outer crust. In a sense, the two dynamic materials briefly couple. Only to decouple after affecting the star's rotational frequency.

If this hypothesis is indeed correct, it means there is a limit on pulsars' moments of inertia. This, in turn, sets a limit on the stars' mass-radius relation. Specifically, the radius must be greater than or equal to 2.9 * GM/c^2.

In time, pulsar glitches will be better understood and will thereby help to explain why these strange stars look and behave the way that they do. Glitches may also be, one day, added to the list of popular science factoids. This will surely delight armchair astronomers the world over.

Sources:
http://www.nature.com/nature/journal/v359/n6396/abs/359616a0.html
https://en.wikipedia.org/wiki/Pulsar
http://astronomy.swin.edu.au/cosmos/G/Glitch