Exotic star

An exotic star is a hypothetical class of compact star that isn't necessarily composed of protons, neutrons, electrons or muons, but relatively stable under gravitational collapse through degeneracy pressure or some other method. Examples of exotic stars include quark stars, strange stars, electroweak stars, boson stars, preon stars, grey holes, and Planck stars. Most described exotic stars are denser than neutron stars, containing materials more dense than degenerate neutronium at their cores and are forms of exotic matter (in the broad sense); but are far less dense than black holes. The most well-understood of exotic stars are the quark stars, which are composed of free quarks in the form of quark-degenerate matter.