Neutron star

A neutron star is the collapsed core of a massive supergiant star. They result from the supernova explosion of a massive star, combined with gravitational collapse, that compresses the core past white dwarf star density, composed mostly of tightly-packed neutrons (neutronium). Some may continue collapsing to form a black hole.

Most neutron stars rotate rapidly, with periods ranging from a few seconds down to milliseconds. Highly energetic neutron stars emit rapid, regular pulses of electromagnetic radiation, and are known as pulsars; the most extreme examples of these objects are known as magnetars.

Neutron stars hold exotic forms of matter called neutronium which is equivalent to a chemical element with atomic number 0, is extremely radioactive, and decays quickly into hydrogen. Some neutron stars can also hold magmatter.

A neutron star merging with another creates immense magnetic fields and short gamma-ray bursts.