What is "quark star"

n. A hypothetical exotic star composed of quark matter.

A quark star is a hypothetical type of compact exotic star composed of quark matter. These are ultra-dense phases of degenerate matter theorized to form inside particularly massive neutron stars.

The hypothesis about quark stars was first proposed in 1965 by Soviet physicists D.D. Ivanenko and D.F. Kurdgelaidze. Their existence has not been confirmed theoretically or astronomically. The equation of state of quark matter is uncertain, as is the transition point between neutron-degenerate matter and quark matter. Theoretical uncertainties have precluded making predictions from first principles. Experimentally, the behaviour of quark matter is being actively studied with particle colliders, but this can only produce very hot (above 10 K) quark-gluon plasma blobs the size of atomic nuclei, which decay immediately after formation. The conditions inside compact stars with extremely high densities and temperatures well below 10 K, can not be recreated artificially so there are no known method to produce, store or study "cold" quark matter directly as it would be found inside quark stars. The theory predicts quark matter to possess some peculiar characteristics under these conditions.