Radio telescope records a rare 'glitch' in a pulsar's regular pulsing beat

April 12, 2018 by Jim Palfreyman, The Conversation
The Vela pulsar makes about 11 complete rotations every second, it also has a glitch. Credit: X-ray: NASA/CXC/Univ of Toronto/M.Durant et al; Optical: DSS/Davide De Martin

Pulsars are rapidly rotating neutron stars and sometimes they abruptly increase their rotation rate. This sudden change of spin rate is called a "glitch" and I was part of a team that recorded one happening in the Vela Pulsar, with the results published today in Nature.

Approximately 5-6% of pulsars are known to . The Vela pulsar is perhaps the most famous – a very southern object that spins about 11.2 times per second and was discovered by scientists in Australia in 1968.

It is 1,000 light-years away, its supernova occurred about 11,000 years ago and roughly once every three years this pulsar suddenly speeds up in rotation.

These glitches are unpredictable, and one has never been observed with a radio telescope large enough to see individual pulses.

To understand what the glitch may be, first we need to understand what makes a pulsar.

Collapsing stars

At the end of a typical star's life, one of three things can happen.

A small star, similar to the size of our Sun, will just quietly expire like a fire going out.

If the star is sufficiently large, a supernova will occur. After this massive explosion the remains will collapse. If the object is sufficiently large then its escape velocity will be greater than the speed of light, and a black hole will be formed.

But if we have a Goldilocks-sized star that is large enough to go supernova, but small enough not to be a black hole, we get a neutron star.

The gravity is so strong that the electrons orbiting the atom are forced into the nucleus. They combine with protons in the nucleus to form neutrons.

These objects are estimated to have a mass of about 1.4 times the mass of our Sun, and a diameter of 20km. The density is such that a cupful of this material would weigh as much as Mt Everest.

They also rotate quite quickly (and very gradually slow down over time) as well as having a massive magnetic field, three trillion times that of the Earth. Electromagnetic radiation emits from both ends of this huge rotating magnet.

Now if one of the poles of this rotating magnet happens to sweep past Earth, we see a brief "flash" in radio waves (and other frequencies too) once every rotation. This is called a pulsar.

The 26m antenna at the Mount Pleasant Radio Observatory. Credit: University of Tasmania, Author provided

The hunt for a 'glitch'

In 2014 I started a serious observing campaign with the University of Tasmania's 26m radio telescope, at the Mount Pleasant Observatory, with a goal to catch the Vela Pulsar's glitch live in action.

I collected data at the rate of 640MB for each 10 second file, for 19 hours a day, for most days over nearly four years. This resulted in over 3PB of data (1 petabyte is a million gigabytes) that was collected, processed and analysed.

On December 12, 2016, at approximately 9:36pm at night, my phone goes off with a text message telling me that Vela had glitched. The automated process I had set up wasn't completely reliable – radio frequency interference (RFI) had been known to set it off in error.

So sceptically I logged in, and ran the test again. It was genuine! The excitement was incredible and I stayed up all night analysing the data.

What surfaced was quite surprising and not what was expected. Right as the glitch occurred, the pulsar missed a beat. It didn't pulse.

The pulse before this "null" was broad and weird. Nothing like I'd ever seen or heard of before.

The two pulses following turned out to have no linear polarisation which was also unheard of for Vela. This meant the glitch had affected the strong magnet that drives the emission that comes from the .

Following the null, a train of 21 pulses arrived early and the variance in their timings was a lot smaller than normal – also very weird.

The glitch explained, sort of

So what causes glitches? The hypothesis that is best supported is that the neutron star has a hard crust and a superfluid core. The outer crust is what slows down, while the superfluid core rotates separately and does not slow down.

This is a very simplified explanation. What really happens is quite complex and involves microscopic superfluid vortices unpinning from the crust's lattice.

After about three years the difference in rotation between the core and crust gets too great and the core "grips" the crust and speeds it up. The data seems to show that it took about five seconds for this speed-up to occur. This is on the faster end of the scale that the theorists had predicted.

All this and other information could help us understand what is called the "equation of state" – how matter behaves at different temperatures and pressures – in a laboratory that we simply cannot create here on Earth.

It also gives us, for the first time, a glimpse into the inside workings of a neutron star.

Explore further: Accretion-powered pulsar reveals unique timing glitch

More information: Jim Palfreyman et al. Alteration of the magnetosphere of the Vela pulsar during a glitch, Nature (2018). DOI: 10.1038/s41586-018-0001-x

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Bhuvanesh
1 / 5 (1) Apr 12, 2018
m
antialias_physorg
5 / 5 (14) Apr 12, 2018
Rough back-of-the-envelope calc: at 20km diameter and 11.2rps the outer part of the inner magnet is cycling at roughly 700km per second.

Now even if the crust just slows down a few percent until it gets 'gripped': speeding that amount of neutron star crust (huge mass!) back up in 5 seconds has....erm...a scary amount of force behind it.

cantdrive85
1.3 / 5 (15) Apr 12, 2018
Rough back-of-the-envelope calc: at 20km diameter and 11.2rps the outer part of the inner magnet is cycling at roughly 700km per second.

Now even if the crust just slows down a few percent until it gets 'gripped': speeding that amount of neutron star crust (huge mass!) back up in 5 seconds has....erm...a scary amount of force behind it.


That is the very reason we know this isn't a spin phenomenon. This is analogous to a relaxation oscillator, it's a relatively simple process and once again goes to show that EE's are more relevant in discussing these things.
691Boat
5 / 5 (9) Apr 12, 2018
Rough back-of-the-envelope calc: at 20km diameter and 11.2rps the outer part of the inner magnet is cycling at roughly 700km per second.

Now even if the crust just slows down a few percent until it gets 'gripped': speeding that amount of neutron star crust (huge mass!) back up in 5 seconds has....erm...a scary amount of force behind it.


That is the very reason we know this isn't a spin phenomenon. This is analogous to a relaxation oscillator, it's a relatively simple process and once again goes to show that EE's are more relevant in discussing these things.

I just asked one of our EE's to model a neutron star with a "crust" and a spinning core to show me the pulses we can observe. He gave me a blank stare. Seems you are incorrect.
yep
1 / 5 (11) Apr 12, 2018
I just asked one of our EE's to model a neutron star with a "crust" and a spinning core to show me the pulses we can observe. He gave me a blank stare. Seems you are incorrect.


Because a core spinning as fast a dentists drill under a crust is as stupid an idea as the extra dense matter of an assumed Neutron star.
jonesdave
5 / 5 (13) Apr 13, 2018
I just asked one of our EE's to model a neutron star with a "crust" and a spinning core to show me the pulses we can observe. He gave me a blank stare. Seems you are incorrect.


Because a core spinning as fast a dentists drill under a crust is as stupid an idea as the extra dense matter of an assumed Neutron star.


Neutron stars are observed, not assumed. Unlike electric stars, electric comets, electric cratering, electric volcanoes,.........etc.
Da Schneib
5 / 5 (8) Apr 13, 2018
@yep, amazingly enough you can see it right above the article; it's that big black rectangle with the blue stuff inside it. We call those things "pictures."
cantdrive85
1 / 5 (5) Apr 13, 2018
Neutron stars are observed, not assumed. Unlike electric stars, electric comets, electric cratering, electric volcanoes,.........etc.

Fraid not snookems, neutron stars are but a fanciful conjecture of plasma morons such as yourself.
theredpill
not rated yet Apr 13, 2018
@yep, amazingly enough you can see it right above the article; it's that big black rectangle with the blue stuff inside it. We call those things "pictures."


Are you claiming the neutron star is visible in the above shot of the pulsar?
jonesdave
5 / 5 (4) Apr 13, 2018
Neutron stars are observed, not assumed. Unlike electric stars, electric comets, electric cratering, electric volcanoes,.........etc.

Fraid not snookems, neutron stars are but a fanciful conjecture of plasma morons such as yourself.


Wrong. Observed in the latest GW detection.
cantdrive85
1 / 5 (4) Apr 13, 2018
Are you claiming the neutron star is visible in the above shot of the pulsar?

There is an object which we can see, but it is not a fanciful anti-scientific neutron star.
cantdrive85
1 / 5 (4) Apr 13, 2018
Wrong. Observed in the latest GW detection.

They discovered how to used statistical gymnastics to support their pseudoscience, that all.
jonesdave
5 / 5 (6) Apr 13, 2018
Are you claiming the neutron star is visible in the above shot of the pulsar?

There is an object which we can see, but it is not a fanciful anti-scientific neutron star.


We've already detected the GWs from one, followed by the EM signature, which matches very well the predictions for neutron stars from theory. Conversely, we just have some Velikovskian crank, claiming they can't exist based on nothing scientific whatsoever, other than his ignorance of all things scientific.
jonesdave
5 / 5 (6) Apr 13, 2018
Wrong. Observed in the latest GW detection.

They discovered how to used statistical gymnastics to support their pseudoscience, that all.


Wrong. How is a detection of GWs, at three different sites any sort of statistical gymnastics? What you mean is that it is beyond your ability to understand, therefore it is like magic for you, and other scientifically illiterate clowns, like the conman Thornhill.
alexander2468
not rated yet Apr 13, 2018
Spinning at 11.2 n/s the glitch speeds up the star to say 11.3n/s it does not appear to say it reverts to 11.2n/s after the glitch settles, It can only speed up if it gets smaller so its gravity gets stronger, its not going to release its grip, this neutron star is gradually increasing its spin!

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