Astrophysical implications of gapless color-flavor locked quark matter: A hot water bottle for aging neutron stars

The gapless color-flavor locked (gCFL) phase is a candidate for the second-densest phase of matter in the QCD phase diagram, making it a plausible constituent of the core of neutron stars. We show that even a relatively small region of gCFL matter in a star will dominate both the heat capacity CV and the heat loss by neutrino emission Lν. The gCFL phase is characterized by an unusual quasiparticle dispersion relation that makes both its specific heat cV and its neutrino emissivity εν parametrically larger than in any other phase of nuclear or quark matter. During the epoch in which the cooling of the star is dominated by direct Urca neutrino emission, the presence of a gCFL region does not strongly alter the cooling history because the enhancements of CV and Lν cancel against each other. At late times, however, the cooling is dominated by photon emission from the surface, so Lν is irrelevant, and the anomalously large heat capacity of the gCFL region keeps the star warm. The temperature drops with time as T∼t-1.4 rather than the canonical T∼t-5. This provides a unique and potentially observable signature of gCFL quark matter.