How does the size of a supernova affect how fast a neutron star spins?

Answer 1

There are several elements to be considered here. First is the mass of the original star, and secondly, its rotational speed. We know that our own Sun spins about once a month; 26 days per rotation in the middle latitudes, but 33 days per rotation nearer the poles.

Thirdly, the law of conservation of angular momentum always applies. The rotational energy in the original star must equal the rotational energies of the resultant neutron star AND the mass blown away into space. (In the explosion of a supernova, only a fraction of the star is compressed into a neutron star or black hole; the majority if the star's mass is thrown into space, where it will eventually be recycled into new stars and planetary systems. This is where the heavy elements that form the Earth came from; old supernova remnants.)

When mass is compressed, such as a star being crushed into a neutron star or black hole - or a spinning ice skater pulling her arms in closer to her body - the angular momentum ALWAYS remains the same. So with a shorter distance between the axis of rotation and the edge, the object must spin more rapidly. The more mass, the faster the spin.

We know that some neutron stars are spinning quite rapidly, because of the radio pulses generated. We call these "pulsating neutron stars" or "pulsars" for short. Each one has its own unique spin, and they generally do not vary. In fact, the radio astronomers who first detected them called them "LGM signals", for "little green men". The astronomers could not imagine how a regular rapid radio pulsation could be generated naturally.