Rotation speed of a neutron star

shounakbhatta

Hello,

Can somebody please tell me in details about the rotation speed of a neutron star? Does it rotate very fast and then slows down?

Thanks.

Chronos

Thats the prevailing opinion. A neutron star retains the angular momentum of the star from which it formed. Because it is so much smaller than its mama, it must spin rapidly to conserve angular momentum. This is where millisecond pulsars come from. Eventually, they will spin down, but this is a very, very slow process. It is not easy to shed angular momentum without invoking unusual circumstances.

ImaLooser

Neutron star rotation ranges up to 50000 rpm. Each star is different. A common pattern is the magnetar, in which a very young neutron star sets up a dynamo that converts most of its rotational speed to a magnetic field. Something like 15% (I forget) of neutron stars are magnetars.

Another common pattern is a star that pulls in matter from a companion. This causes the star to "spin up' and reach extreme rotations. The limit is that at superhigh rotation the star becomes asymmetrical and emits gravitational waves. Maybe 5% of neutron stars are like this.

Isolated neutron stars will eventually slow down, but this takes a very, very long time.

shounakbhatta

Hello,

What is meant by a magnetar?

Mordred

A type of neutron star

http://en.wikipedia.org/wiki/Magnetar

Chronos

A magnetar is a neutron star, generally believed to be relatively young, with an incredibly powerful magnetic field. Most neutron stars are believed to have strong magnetic fields, a magnetar has an unusually powerful magnetic field.

ImaLooser

The Earth has a magnetic field of about half a gauss. An ordinary neutron star is about a billion gauss, which I find inconceivable. A magnetar has maybe a quadrillion gauss, and is limited to that only because electron-positron pairs start to form spontaneously in the vacuum and carry off the energy. Inside the magnetar the pairs are inhibited by the matter, so it is thought that a quintillion gauss is possible. The magnetic field can be so strong that it changes the shape of atomic nuclei, polymerizes them, and noticeably changes the shape of the star.

The highest magnetic field ever generated on Earth was about ten million gauss, produced momentarily via an explosion. A hundred thousand gauss is enough to levitate a frog.

Mordred

I don't suppose you know what type of radiation/perturbation that particle production would fall under. I'm currently studying Hawking, Unruh, Parker and false vacuum particle production so I am curious which this form of particle production this one would best fall under.

Chronos

That would be the Schwinger pair production mechanism.

Mordred

Thanks Chronos