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. The fastest rotate over 700 times a second, and combined with such dense gravities should emit gravitational waves. 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. A neutron star merging with another creates immense magnetic fields and short gamma-ray bursts.

Neutron stars hold exotic forms of matter:

 * Neutronium which is equivalent to a chemical element with atomic number 0, has zero protons or electrons, is extremely radioactive, and decays quickly into hydrogen. This is so dense that a sugar cube could contain the mass of the entire human population. Neutronium matter can degenerate into degenerate matter or strange matter (during core collapse) which is much denser.
 * Degenerate matter is neutron degeneracy with a density magnitude of 1017 kg/m3, or up 1018 kg/m3 in the core.
 * Strange matter is quark matter containing strange quarks in the core of many neutron stars, varying in size from femtometers (strangelets) to kilometers. Strange matter has a density magnitude of 1017 kg/m3, whereas ordinary atoms are in the picoscale range (1012 kg/m3). A neutron star with a quark matter core is a hybrid star or strange star.
 * Magmatter is denser, at around 1018 kg/m3, formed in the core during the stages of collapse into a black hole, and monopoles are released as radiation.