Stare at a few pulsars for long enough and one of them will twitch. What you’ll see is a sudden jump in the frequency of the radio pulses they produce. For some reason, the pulsar has speeded up.
Astronomers call these events glitches and they are exceedingly rare. In the 40 years since pulsars were discovered, astronomers have discovered some 1800 pulsars but recorded only 170 glitches in 51 of them.
Today, these figures change significantly with the announcement by Jian-Ping Yuan and buddies that in the last ten years or so, the Nanshan radio telescope at Urumqi Observatory in China has seen another 29 glitches in 19 young pulsars.
That’s a significant body of data. For astrophysicists, glitches are important because they ought to give a unique insight into the internal dynamics of pulsars, spinning neutron stars with a magnetic field so powerful that they emit a beam of radio waves along the axis of the magnetic field.
Because of a mismatch between the star’s axis of rotation and the axis of the magnetic field, the beam sweeps across the sky like a lighthouse. Astronomers see just those that happen to be pointing our way.
Over time, pulsars slow down as they dissipate energy so any sudden increase in rotation speed is odd. Their are two theories for why this happens. One is that the change in rotation is caused by a crustal starquake, a redistribution of stress in the star’s outer shell that had previously built up as the star’s rotation rate slowed down.
The second is that these stresses may pin down vortices in the star’s superfluid interior. The sudden unpinning of these vortices causes an increase in the rotation rate.
Either way, glitches ought to provide some insight into how that happens.
But not yet. One feature of glitches which the Chinese data confirms is that they are far more complex than you might expect. Their size, the interval between them and the rate at which the star slows down afterwards all show complex patterns of behaviour that so far cannot be explained.
That means the inner workings of pulsars will remain a mystery until some enterprising astrophysicist comes up with a theory that explains the complex behaviour of glitches.