Formation Of Quark Matter In Neutron Stars

Abstract

At very large densities and/or temperatures a quark-hadron phase transition is expected to take place. Simulations of QCD on lattice at zero baryon density indicate that the transition occurs at $T_c \sim 150-170$ MeV. The calculations indicate that transition is likely to be second order or a cross over phenomenon. Although the lattice simulations have not given any indication on when the transition occurs at nonzero baryon density, the transition is expected to occur around the densities of few times nuclear matter density. Also, there is a strong reason to believe that the quark matter formed after the phase transition is in colour superconducting phase. The matter densities in the interior of neutron stars are expected to be several times the nuclear matter density and therefore the neutron star cores may possibly consist of quark matter. One then expects that this quark matter is formed during the collapse of supernova. Starting with the assumption that the quark matter, when formed consists of predominantly u and d quarks, we consider the evolution of strange quarks by weak interactions in the present work. The reaction rates and time required to reach the chemical equilibrium are computed here. Our calculations show that the chemical equilibrium is reached in about $10^{-7}$ seconds. Further more during and immediately after the equilibration process enormous amount of energy is released and copious numbers of neutrinos are produced. We show that for reasonable models of nuclear equations of state the amount of energy released could be as high as $10^{53}$ ergs and as many as $10^{58}$ neutrinos may be emitted during the quark matter formation.