How a Pulsar Gets Its Spin

brian0918 writes "Until now, the assumption has been that the rapid spin of a pulsar comes from the spin of the original star. The problem was that this only explained the fastest observed pulsars. Now, researchers at Oak Ridge have shown that the spin of a pulsar is determined by the shock wave created when the star's massive iron core collapses. From the article: 'That shock wave is inherently unstable, and eventually becomes cigar-shaped instead of spherical. The instability creates two rotating flows — one in one direction directly below the shock wave and another, inner flow, that travels in the opposite direction and spins up the core. The asymmetrical flows establish a 'sloshing' motion that accounts for the pulsars' observed spin velocities from once every 15 to 300 milliseconds.'"

Comments

Pulsar gets it's spin

[DittoBox]

For each and shock that waves
Another Pulsar gets it's spin
So show you care and let your iron core collapse
And help a pulsar spin tonight...

Bad reporting

[exp(pi*sqrt(163))]

From 'the first plausible explanation' to 'researchers at Oak Ridge have shown that the spin of a pulsar is determined by the shock wave created when the star's massive iron core collapses'. Shows how poor journalists give scientists a bad name by making their claims seem much stronger than they are. The press release is very careful in how it makes its statements. The /. story isn't.

Re:Not trying to discredit....

[servognome]

But it seems that most of these science articles, particularly the ones related to astronomy, have forgotten the word "theory".

All science is theory, so it would be redundant.

Re:Pulsars as GPS

[mrcaseyj]

I think the idea of Pulsar GPS is primarily intended for interplanetary spacecraft. For terrestrial stuff GPS probably works better. One problem with Pulsars is that you would have to know which pulse to measure the time difference relative to the other Pulsars. if a pulsar pulses every 300ms then the pulses will be about a third of a light second apart or about 100km. If you go 100km relative to the pulsar you might get mixed up as to which pulse to lock onto and think you hadn't moved. The problem gets worse as the pulse rate gets higher. GPS doesn't have this problem because the absolute time is encoded within the signal from each satellite so you know the date and time each pulse left the GPS satellite.

One way to deal with the problem is to carefully keep continuous track of your position so you can keep straight which pulse to measure. If you can figure out where you are accurately enough by some other means you can figure out which pulse to measure. You can decrease the uncertainty of which pulse to use by using more than four pulsars. For example if one pulsar pulses every 7ms and another pulses every 11ms you can increase your window to 77ms by watching as they go into and out of sync.

I'm guessing that another problem is that the pulsars probably have a rather faint signal. You may have to have four or more large high gain dish antennas pointed in different directions to pick up the signals. This would be impractical on earth for most applications and would be a lot of extra weight for a spacecraft also. You might be able to have just one dish and point it at each pulsar in turn.

I don't see anything about this on Wikipedia. I think I'll add it one of these days.

Or, in legal circles...

[mangu]

"theory" is for science journalists as "allegedly" is for the crime pages. We all know it's true, but no one wants to risk the liability of a libel and slander suit.

Re:Strange summary...

[iamlucky13]

Thanks for explaining that.

However, the submission and the article are still a little strange in their word choices (mostly the submission...If you re-read the article a few times, it makes more sense). They seem to suggest that the assymetric shockwave gives the pulsars their sping, when according to the theory, it actually takes away spin. I clicked on the article wondering how in the world they were postulating massive, exploding objects with very low or possibly non-existant angular momentums.

If I'm reading it right, the ejected debris from the rebound should spiral more in this case to account for the net loss of angular momentum, no?

Anyway, the worst part was this line:

According to three-dimensional simulations they performed at the Leadership Computing Facility, located at ORNL, the spin of a pulsar is determined not by the spin of the original star, but by the shock wave created when the star's massive iron core collapses.

What they really meant is the original spin plus the shockwave, not just the latter instead of the former. Other than that though, the press release is a fresh breath of clear writing.

Re:Pulsars as GPS

[iluvcapra]

a third of a light second apart or about 100km

I think you mean 100,000 km.

If you go 100km relative to the pulsar you might get mixed up as to which pulse to lock onto and think you hadn't moved.

You wouldn't use the phase of the pulsar signal to get a distance reading, but you could use it's frequency as a way of identifying it uniquely, and then you would triangulate your position by getting a bearing on three or four pulsars; this is essentially how the starburst pattern on the Mariner Plaque is supposed to work for aliens trying to find Earth. It gives the frequency of pulsars near the earth and their bearing to Sol relative to the galactic center. The aliens would identify the pulsars by their frequency, and then use their knowledge of the pulsars' absolute locations to work backward and triangulate the position of Sol (assuming these aliens, a million years from now, are able to backtrack the locations of all the pulsars, as they will all have moved relative to Sol and will have slowed down in their spinning, causing an error in our reported frequencies).