Researchers find a 'glitch' in pulsar 'glitch' theory

Dec 18, 2012
The Vela supernova remnant at optical wavelengths (Credit: CTIO/AURA/NSF), with location of the Vela pulsar indicated. Inset: Artist's impression of the pulsar’s interior, and the interaction between superfluid vortices and the nuclei that make up the star’s crust.

(Phys.org)—Researchers from the University of Southampton have called in to question a 40 year-old theory explaining the periodic speeding up or 'glitching' of pulsars.

A pulsar is a highly magnetised rotating neutron star formed from the remains of a supernova. It emits a rotating beam of , which can be detected by powerful telescopes when it sweeps past the Earth, rather like observing the beam of a lighthouse from a ship at sea.

Pulsars rotate at extremely stable speeds, but occasionally they speed up in brief events described as 'glitches' or 'spin-ups'. The prevailing theory is that these events arise as a rapidly spinning within the star transfers rotational energy to the star's crust, the component that is tracked by observations. However, Southampton academics have used a to disprove this.

Professor Nils Andersson explains: "Imagine the pulsar as a bowl of soup, with the bowl spinning at one speed and the soup spinning faster. between the surface of the bowl and its contents, the soup, will cause the bowl to speed up. The more soup there is, the faster the bowl will be made to rotate.

"This analogy describes the concept behind the accepted theory of why pulsars suddenly increase speed or 'spin-up'. However, our research shows that these pulsar glitches are too large to be explained in this way. The amount of superfluid, or 'soup', available in the crust of a pulsar is too small to cause the kind of friction needed to create this effect."

Professor Andersson and Dr Wynn Ho from the University of Southampton used their calculations, in conjunction with data from and recent results from nuclear physics theory, to challenge current thinking on this subject.

The Southampton researchers have written a paper detailing their theory, produced in collaboration with Kostas Glampedakis at the Universidad de Murcia, Spain and Cristobal Espinoza at the University of Manchester. It is published in Physical Review Letters.

Explore further: Image: Galactic wheel of life shines in infrared

More information: Pulsar Glitches: The Crust is not Enough, N. Andersson, K. Glampedakis, W. C. G. Ho, and C. M. Espinoza, Phys. Rev. Lett. 109, 241103 (2012) physics.aps.org/synopsis-for/1… ysRevLett.109.241103

Synopsis: A Pulsar's Inner Secrets: physics.aps.org/synopsis-for/1… ysRevLett.109.241103

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User comments : 7

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jsdarkdestruction
5 / 5 (7) Dec 18, 2012
very interesting, i can tell you what its not though. secret alien codes describing a galactic superwave and subquantum kinetics to paul laviolette.
Parsec
5 / 5 (4) Dec 18, 2012
very interesting, i can tell you what its not though. secret alien codes describing a galactic superwave and subquantum kinetics to paul laviolette.

LOOLOLOL... I suspect your quite right.
omatwankr
3.9 / 5 (7) Dec 18, 2012
"i can tell you what its not though. secret alien codes describing a galactic superwave and subquantum kinetics to paul laviolette"

So we are in agreement that it is caused by Repugnant Newtrons I commune with while chasing the ether-wave dragon
Widdekind
1 / 5 (2) Dec 19, 2012
Inexpertly, a sudden increase in spin rate implies a sudden contraction in size ("ice skater pulling arms in"). Pulsars are born as the hot embers of SNe. Presumably, pulsars cool off over the ages. Perhaps a dense, high-pressure solid, cooling down, on a Pressure-Temperature diagram, could conceivably cross solid-state phase transitions, like water ice X to IX to VIII to VII etc.? Perhaps neutronized "neutronium" matter exists in several solid phases, of increasing density, so that as the pulsars cool across phase transitions, they suddenly shrink ?
GSwift7
3 / 5 (4) Dec 19, 2012
Inexpertly, a sudden increase in spin rate implies a sudden contraction in size ("ice skater pulling arms in").


You have it backwards. The glitches are when they slow down for a short time, then they speed back up to almost the speed they had before the glitch.

That aside, your idea is plausible, but in the opposite direction. I was thinking that the radius might expand, slowing it down, then the star settles back down and re-compacts, returning to its original rotation rate. This could be achieved by the star flattening out a bit around its equator for a short time.

In the above article, I think they place way too much emphasis on the 'accepted theory'. It seems more accurate to say that this is currently unexplained, though there is one idea that is being investigated more than others, and has gained some support.
Fleetfoot
5 / 5 (4) Dec 20, 2012
Inexpertly, a sudden increase in spin rate implies a sudden contraction in size ("ice skater pulling arms in").


You have it backwards. The glitches are when they slow down for a short time, then they speed back up to almost the speed they had before the glitch.


I don't that's the common type of glitch, see for example Figure 3 in this paper:

http://arxiv.org/...43v2.pdf

Similarly figures 2(a) and 3(a) in this show the same sudden increase in frequency, not a decrease. The text bears this out too:

"The first glitch in PSR 1046-58 was observed in this monitoring programme. It occurred on December 9, 1997, about 200 days after the commencement of intensive observations on this pulsar. The spin-up was rather large in magnitude and was accompanied by an increase in spin-down rate."
ValeriaT
1 / 5 (1) Dec 20, 2012
There are two physical mechanisms thought to be responsible for the glitch of a pulsar - either they are caused by starquakes, in which case the neutron star's crust cracks, and there is a fundamental reorganisation of the matter within the star, or they are due to a catastrophic unpinning of vortices in the neutron star superfluid. Young, energetic pulsars like the Crab are thought to undergo starquakes whereas those of more intermediate age (~104-5 yr) are thought to glitch because of an unpinning of the vortices in the neutron star superfluid. Both the Crab and Vela pulsars glitch regularly. Millisecond pulsars and those with large characteristic ages rarely if ever glitch.