Pulsars are rapidly rotating neutron stars observed to have pulses of radiation at very regular intervals that typically range from milliseconds to seconds. If parts of the neutron star interior start to move outwards, the star spins faster. This is called a ‘glitch,’ and it’s providing astronomers with a brief insight into what lies within these objects. In a new study, a team of astronomers from Monash University, the ARC Centre of Excellence for Gravitational Wave Discovery (OzGrav), McGill University, and the University of Tasmania, analyzed data from the 2016 glitch of a neutron star known as the Vela pulsar.
The Vela pulsar, a neutron star that was formed when a massive star collapsed. Image credit: NASA / CXC / University of Toronto / M. Durant et al / DSS / Davide De Martin.
About 5-6% of pulsars are known to glitch. Discovered by Australian astronomers in 1968, the Vela pulsar is perhaps the most famous.
This pulsar is located in the constellation Vela, approximately 1,000 light-years away.
It spins about 11.2 times per second, and is known to glitch about once every three years.
“The glitch itself is quick, less than 12 seconds,” said Dr. Jim Palfreyman, an astronomer with the University of Tasmania.
“But just before it glitches, it actually dips in speed, then overshoots, then decelerates to a faster than normal speed.”
By analyzing data from a recent glitch event in the Vela pulsar, observed by the Mount Pleasant radio telescope on December 12, 2016, Dr. Palfreyman and colleagues found that the glitching star started spinning faster than previously observed, before relaxing down to a final state.
“This observation gives scientists the first-ever detailed glimpse into the interior of the star, revealing that the inside actually has three different components,” said Dr. Paul Lasky, an astronomer at Monash University.
“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.”
“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.”
This overshoot has been predicted by researchers, but had never been observed until now.
“Immediately before the glitch, we noticed that the star seems to slow down its rotation rate before spinning back up,” said Dr. Greg Ashton, a researcher at Monash University and OzGrav.
“We actually have no idea why this is, and it’s the first time it’s ever been seen!”
“We speculate it’s related to the cause of the glitch, but we’re honestly not sure.”
The findings appear in the journal Nature Astronomy.
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Gregory Ashton et al. Rotational evolution of the Vela pulsar during the 2016 glitch. Nature Astronomy, published online August 12, 2019; doi: 10.1038/s41550-019-0844-6
