A Hot Water Bottle for Aging Neutron Stars

Abstract

The gapless color-flavor locked (gCFL) phase is 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 C_V and the heat loss by neutrino emission L_ν. The gCFL phase is characterized by an unusual quasiparticle dispersion relation that makes both its specific heat c_V and its neutrino emissivity epsilon_νparametrically 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 C_V and L_νcancel against each other. At late times, however, the cooling is dominated by photon emission from the surface, so L_νis irrelevant, and the anomalously large heat capacity of the gCFL region keeps the star warm. The temperature drops with time as T\sim t^{-1.4} rather than the canonical T\sim t^{-5}. This provides a unique and potentially observable signature of gCFL quark matter.

14 pages, 5 figures. v2: Error corrected, with implications visible in Fig. 2, but not in Figs. 3,4,5. No changes to final results or conclusions