It turned out that a strange hiccup in a dead star’s rotational speed was even more exciting than we assumed. Astronomers showed for the first time that the Vela pulsar’s rotation slowed instantly before its 2016 glitch. So, how close are we in revealing the mystery of glitching pulsar.
This was not only totally unexpected, but it could also assist us to narrow down the mysterious dynamics in the neutron stars ultra-dense interiors. Some of the most helpful objects in the Universe are fast rotating neutron stars known as pulsars for astronomers. They flash a radiation beam like a lighthouse as they rotate, often on extremely fast and regular timescales.
This may be helpful for a variety of scientific applications, but even pulsars are not 100% accurate. They gradually lose a tiny amount of rotational energy over time, slowing down ever-so-slightly. But they can suddenly speed up now and then before they return to normal. That’s what we call a glitch.
We don’t understand what causes the pulsar to glitch, but astronomers think it has something to do with the internal processes of the neutron star.
And that’s where the Vela pulsar comes in, located about 1,000 light-years from Earth. It usually spins at around 11 rotations per second. But it’s also a well-known serial glitch that hiccups about once every three years. (Its recent glitch occurred in February of this year, but it concerns the previous glitch in December 2016.)
These glitches cannot be predicted, but their relative regularity means that we have a better chance of catching one in the act, which is what happened in December 2016, when the glitch was first recorded using a radio telescope in real-time.
During the glitch event, the first evaluation of this glitch disclosed changes in the pulse shape. Now a closer analysis has disclosed that the pulsar starts spinning even faster during the glitch-what is known as an overshoot of rotational frequency-and then relaxes back to a more normal speed pretty rapidly.
This is compatible with theoretical models suggesting the inner structure of a neutron star is composed of three components.
“One of these components, a soup of superfluid neutrons in the crust’s inner layer, moves out first and hits the star’s rigid outer crust, causing it to spin up,” said astrophysicist Paul Lasky of Monash University in Australia.
“But then, a second superfluid soup moving in the heart catches up to the first one causing the star’s spin to slow down. This overshoot was anticipated a few times in the literature, but this is the first real moment it was recognized in observations.”
It’s not conclusive evidence that this is actually what’s going on inside neutron stars, but it brings us a little nearer to narrowing it down.
However, the slowdown we mentioned previously still defies explanation. In their document, the scientists observed that the slowdown may effectively cause the glitch by creating a critical lag between the crust and the crustal superfluid, but a gigantic question mark still hangs over it.
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“We noticed immediately before the glitch that the star appears to slow down its rotation rate before spinning back up,” said astronomer and physicist Greg Ashton of Monash University.
“We don’t know why this is, and it’s been seen for the first time.”
However, while the mystery remains, the analysis shows that the glitch is a little more complicated than a brief single-step process. The team hopes that new explanations for the dynamics they have uncovered will come up for future observations, analysis and theoretical modelling.
The research has been published in Nature Astronomy.