A Glitch In A Neutron Star Allowed Astronomers To "Peek" At Its Interior

The Vela Pulsar. X-ray: NASA/CXC/Univ of Toronto/M.Durant et al; Optical: DSS/Davide De Martin

The Vela Pulsar is a peculiar neutron star that spins on its axis every 89.33 milliseconds. At the time of its discovery, it was the fastest-rotating pulsar ever found, and while that it is no longer the case, researchers have identified other properties that make it pretty special. In particular, the pulsar glitches.

On December 12, 2016, the Vela Pulsar was caught glitching live by researchers on-site. The Mount Pleasant Radio Observatory captured the star going from its constant spinning to a more chaotic one. The Telescope witnessed a broad pulse, followed by a missing one, and then two short ones whose emissions were linearly polarized.

A team of researchers have now reanalyzed the data collected in 2016 and uncovered some new facts about the glitch. As reported in Nature Astronomy, the star's rotation sped up during the glitch before going back down to the usual level. The scientists were able to better constrain the whole event, finding that it took less than 12.6 seconds to develop. They then used the new constraints to improve models of the interior of pulsars.

Many questions remain regarding the interior of these defunct stars, essentially those with incredibly dense collapsed cores from stars that went supernova. In their interiors, matter gets into all kinds of weird states. Researchers think that the interaction between the extremely hard crust and its peculiar superfluid layers below is responsible for the glitch. This work suggests that three components are at work here.

"One of these components, a soup of superfluid neutrons in the inner layer of the crust, moves outwards first and hits the rigid outer crust of the star causing it to spin up," co-author Dr Paul Lasky, from Monash University, said in a statement. "But then, a second soup of superfluid that moves in the core catches up to the first causing the spin of the star to slow back down.”

The team also saw something that wasn’t expected, and based on what we know about neutron stars, shouldn’t have happened.

"Immediately before the glitch, we noticed that the star seems to slow down its rotation rate before spinning back up," added lead author Dr Greg Ashton, also at Monash. "We actually have no idea why this is, and it's the first time it's ever been seen. It could be related to the cause of the glitch, but we're honestly not sure."

Hopefully, some theoretical physicist can use this data to improve our models. And if more data is needed, the Vela Pulsar is ready to supply: It tends to have a glitch roughly every three years.

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