A neutron star is the collapsed remnant of a Type II or Ib supernova.
It has an structure than begins with an iron layer on the outside, going to atoms with increasingly more neutrons to the inside. The core is believed to be a superdense matter, whose exact nature is still not well understood. Some researchers refer to this theoretical substance as neutronium. It could be a superfluid mixture of neutrons with a few protons and electrons, other high energy particles may be present, and even sub-atomic quark matter is possible.
Some neutron stars than can be observed are:
- Pulsar - general term for neutron stars that emit radiation at regular intervals.
Neutron stars rotate extremely rapidly after their creation due to the conservation of angular momentum; like an ice skater pulling in his arms, the slow rotation of the original star's core speeds up as it shrinks. A newborn neutron star can rotate up to several thousand times per second, distorting into an oblate spheroid shape despite its own immense gravity. Over time, however, neutron stars slow down due to drag on their magnetic fields; older neutron stars may take several seconds or minutes for each revolution.