Exotic star
An exotic star is a hypothetical compact star composed of exotic matter (something not made of electrons, protons, neutrons, or muons), and balanced against gravitational collapse by degeneracy pressure or other quantum properties.
Types of exotic stars include
- quark stars (composed of quarks)
- strange stars (composed of strange quark matter, a condensate of up, down, and strange quarks)
- § Preon stars (speculative material composed of preons, which are hypothetical particles and "building blocks" of quarks, should quarks be decomposable into component sub-particles).
Of the various types of exotic star proposed, the most well evidenced and understood is the quark star.
In Newtonian mechanics, objects dense enough to trap any emitted light are called dark stars,, as opposed to black holes in general relativity. However, the same name is used for hypothetical ancient "stars" which derived energy from dark matter.
Exotic stars are largely theoretical – partly because it is difficult to test in detail how such forms of matter may behave, and partly because prior to the fledgling technology of gravitational-wave astronomy, there was no satisfactory means of detecting cosmic objects that do not radiate electromagnetically or through known particles. It is not yet possible to verify novel cosmic objects of this nature by distinguishing them from known objects. Candidates for such objects are occasionally identified based on indirect evidence gained from observable properties.