Exotic star

An exotic star is a hypothetical or unusual compact star whose internal structure depends on matter beyond ordinary neutron-rich nuclear matter, such as quark matter or bosonic matter.

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Neutron star: A compact stellar remnant supported mainly by the pressure of neutron-rich matter. It provides the standard dense-matter baseline that exotic-star models extend.
Quark star: A hypothetical compact star composed largely or entirely of deconfined quark matter. It is the best-known exotic-star proposal based on a new phase of hadronic matter.
PSR J0740+6620: A rapidly rotating millisecond pulsar with a mass near twice that of the Sun. Its high mass constrains equations of state proposed for quark and hybrid stars.
White dwarf: A stellar remnant supported against gravity mainly by electron degeneracy pressure. Its lower density and electron-supported structure differ sharply from exotic compact-star proposals.
Equation of state: A relation connecting pressure, density, and other thermodynamic properties of matter. It determines whether a proposed exotic interior can support a star against gravity.
Strange star: A hypothetical star made of stable strange quark matter, possibly extending to its surface. The strange-matter hypothesis predicts a specific kind of self-bound quark star.
PSR J0030+0451: A nearby millisecond pulsar whose mass and radius were constrained by NICER X-ray observations. Its measured properties test whether compact-star models permit unusual interiors.
Black hole: A region of spacetime from which no signal can escape beyond its event horizon. Unlike an exotic star, a black hole has no stable material surface outside its horizon.
Tolman–Oppenheimer–Volkoff equation: The relativistic hydrostatic-equilibrium equation for a spherical, nonrotating star. It translates an exotic-matter equation of state into stellar structure and maximum mass.
Boson star: A hypothetical self-gravitating configuration of bosonic fields, without a conventional material surface. It replaces neutron-rich matter with a coherent bosonic field as the source of stellar structure.