Color Superconductivity and Blinking Proto-Neutron Stars

Due to instabilities at the Fermi surface, matter composed of deconfined quarks is believed to be a color superconductor at low temperatures (see Refs. [1] and other reviews). While the precise value of the energy gap at astrophysical densities is yet indeterminate, calculations using models of vacuum physics generally predict a gap in the neighborhood of 100 MeV for densities at and above three times that of equilibrium nuclear matter. This implies that quark matter with a chemical potential fixed around 400 MeV undergoes a phase transition between a quark-gluon plasma state and one of paired quarks at a critical temperature near 50 MeV. In this talk I discuss how this could lead to a variation in the neutrino signal emanating from a proto-neutron star formed in the wake of a supernova. Our current understanding of Type II (core collapse) supernovae, based on a handful of observations and quite a bit of theoretical modeling, begins with the implosion of the inner core of star of mass 8–20 solar masses (see Ref. [2] for a recent review). The evolution of the remnant proto-neutron star is driven by the diffusion of neutrinos, which make their way through the hot (T ∼ 25 MeV) and dense (nB ∼ 3n0) core matter before a few are eventually detected on Earth. The temporal characteristics of this signal are determined for the most part by the neutrino mean free path through this core. For temperatures much lower than the superconducting energy gap, T ≪ ∆, quark states are replaced by diquark quasi-particles and neutrino-quark cross sections are exponentially suppressed. Thus at late times, when T ∼ 1 KeV, the neutrino mean free path in quark matter is practically infinite. But within the first minute after core collapse, deleptonization heats the dense core to T ≃ 50 MeV before thermal neutrino emission cools the system. It is during this time that transitions between states of strongly-interacting matter would occur. While the phase transition from hadronic matter to a quark plasma is likely first order (but poorly understood), a slightly later transition from quark to superconducting quark matter might be second order, as in