Cooling of Quark Stars in the 2 SC Phase Effect of Photons from Glueball decay

The cooling history of a quark star in the 2-flavour color superconductive (2SC) phase is investigated. In particular the novel process of photon generation via glueball (GLB) decay in the 2SC phase is taken into account. As much as 10−10 erg of energy is provided by the GLB decay. This source of photons fundamentally intrinsic to quark matter in the 2SC phase is unique to our model. The generated photons slowly diffuse out of the quark star keeping it hot and radiating as a perfect black-body for millions of years. The blackbody spectra of isolated neutron stars such as RX J185635-3754, RX J0720.4-3125 and AXPs resembling 4U 0142+61 and its featureless nature can naturally be accounted for in our model if these are quark stars in the 2SC phase with the GLB decay mechanism at play. Fits to observed data favor models with superconductive gaps of ∆2SC ∼ 15-35 MeV and densities ρ2SC = (2.5-3.0) × ρN (ρN being the nuclear matter saturation density) for quark matter in the 2SC phase. If correct, our model combined with observations of isolated compact stars could provide vital information to studies of quark matter and its exotic phases. The picture presented here can be generalized to quark stars entering a superconductive phase where photon generation mechanisms are at play.