A remnant star of a supernova explosion with an approximate size of the sun or larger , in which gravity has caused all matter to collapse into a giant nucleus composed only of neutrons. The collapse greatly amplifies any magnetic field present in the pre-collapse star, as well as speeds up the rate of rotation significantly.

It is believed that pulsars, pulsating radio sources with very precise pulsation periods, are neutron stars of radius about 10 km and rotation period about 1 second. Their magnetic axis spins and beams radio waves, in a way similar to the way a lighthouse beams its light.