Archive of Astronomy Questions and Answers

What is a starquake?

When pulsars were first discovered by radio astronomers in the 1960's, they found that these ultra-precise time keepers would occasionally, and very suddenly, spin faster. Theoreticians who studied pulsars and the underlying, spinning neutron stars which caused them, concluded that these dense stellar cinders would probably consist of a thin crust a few meters thick, floating on top of an even stranger core of collapsed neutron matter. This crust would probably be quite unstable mechanically because of the incredible gravitational and rotational stresses it was feeling. Like Earth's crust, the neutron star crust could suddenly snap, but the result would be that the neutron star would settle into an even denser, more compact shape which means it would also have to spin slightly faster to conserve its original angular momentum. So, these crustal glitches, soon became known as 'starquakes' for obvious reasons. The above figure from The University of Chicago has the following caption:

A magnetized neutron star suffers a starquake. The starquake creates a fault on the crust surface that begins at the equator and spreads towards the magnetic poles. Matter moves along the faults from the equator to higher latitudes, forming mountains. These mountains break the symmetry of the star, causing it to wobble. When the wobbling stops, the star's magnetic field will be tilted even farther away from its rotation axis causing an increase in the rate at which the star slows down. Such increases in spin-down rate have been observed in at least 3 pulsars following a sudden spin-up, and accompany small increases in the star's spin rate known as "glitches". In the case of the pulsar in the Crab nebula, this effect was known soon after its discovery in 1968 but it remained unexplained until now.