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 and leptons, 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, although its existence is not confirmed.

In Newtonian mechanics, objects dense enough to trap any emitted light are called dark stars,^[1]^[2]^[a], 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 hypothetical – 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 compact astrophysical objects that do not radiate either electromagnetically or through known particles. While candidate objects are occasionally identified based on indirect evidence, it is not yet possible to distinguish their observational signatures from those of known objects.

^ Visser, Matt; Barcelo, Carlos; Liberati, Stefano; Sonego, Sebastiano (February 2009). "Small, dark, and heavy: But is it a black hole?". arXiv:0902.0346v2 [gr-qc]. Visser, Matt; Barcelo, Carlos; Liberati, Stefano; Sonego, Sebastiano (2009). "Small, dark, and heavy: But is it a black hole?". arXiv:0902.0346v2 [gr-qc].
^ ^a ^b Visser, Matt; Barcelo, Carlos; Liberati, Stefano; Sonego, Sebastiano (30 September 2009). "How quantum effects could create black stars, not holes". Scientific American. No. October 2009. Archived from the original on 15 November 2013. Retrieved 25 December 2022. Originally published with title "Black Stars, Not Holes".

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[1] Visser, Matt; Barcelo, Carlos; Liberati, Stefano; Sonego, Sebastiano (February 2009). "Small, dark, and heavy: But is it a black hole?". arXiv:0902.0346v2 [gr-qc]. Visser, Matt; Barcelo, Carlos; Liberati, Stefano; Sonego, Sebastiano (2009). "Small, dark, and heavy: But is it a black hole?". arXiv:0902.0346v2 [gr-qc].

[Visser-Barcelo-etal-2009-SciAm-2] Visser, Matt; Barcelo, Carlos; Liberati, Stefano; Sonego, Sebastiano (30 September 2009). "How quantum effects could create black stars, not holes". Scientific American. No. October 2009. Archived from the original on 15 November 2013. Retrieved 25 December 2022. Originally published with title "Black Stars, Not Holes".

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