User: Shitok

Spindowns

On: How a Pulsar Gets Its Spin

I think the story ought to acknowledge the larger effect which comes from the stars initial angular momentum.

Our Sun (for example) rotates at the rate of around once per 25 days and has a radius of around 1 million km. If
it was to collapse into a neutron star without losing any mass the moment of inertia would go down by a factor
of (1,000,000 km/10 km)^2 = 10 billion. So the rotation rate would go up to 4500 times per second. The principle
is the same one that makes figure skaters spin-up when they bring their arms and legs closer to their bodies.

Clearly, it would not retain all of its matter when collapsing and you need to be several times heavier than the
sun in order to collapse into a neutron star. The fastest pulsars still only rotate at ~600x per second. But its
still a significant factor in the spin rate calculation.

Of course, then they spin down becomes of electromagnetic radiation. Some of them probably even spin down because
they are asymmetric and lose energy in the form of gravitational radiation.