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

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: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.