Evolution of proto-neutron stars

We study the thermal and chemical evolution during the Kelvin-Helmholtz pha se of the birth of a neutron star, employing neutrino opacities that are co nsistently calculated with the underlying equation of state (EOS). Expressi ons for the diffusion coefficients appropriate for general relativistic neu trino transport in the equilibrium diffusion approximation are derived. The diffusion coefficients are evaluated using a held-theoretical finite-tempe rature EOS that includes the possible-presence of hyperons. The variation o f the diffusion coefficients is studied as a function of EOS and compositio nal parameters. We present results from numerical simulations of proto-neut ron star cooling for internal stellar properties as well as emitted neutrin o energies and luminosities. We discuss the influence of the initial stella r model, the total mass, the underlying EOS, and the addition of hyperons o n the evolution of the proto-neutron star and on the expected signal in ter restrial detectors. We find that the differences in predicted luminosities and emitted neutrino energies do not depend much upon the details of the in itial models or the underlying high-density EOS for early times (t < 10 s), provided that opacities are calculated consistently with the EOS. The same holds true for models that allow for the presence of hyperons, except when the initial mass is significantly larger than the maximum mass for cold,ca talyzed matter. For times larger than about 10 s, and prior to the occurren ce of neutrino transparency, the neutrino luminosities decay exponentially with a time constant that is sensitive to the high-density properties of ma tter. We also find the average emitted neutrino energy increases during the first 5 s of evolution and then decreases nearly linearly with time. In ge neral, increasing the proto-neutron star mass increases the average energy and the luminosity of neutrinos, as well as the overall evolutionary timesc ale. The influence of hyperons or variations in the dense matter EOS is inc reasingly important at later times. Metastable stars, those with hyperons t hat are unstable to collapse upon deleptonization, have relatively long evo lution times, which increase the nearer the mass is to the maximum mass sup portable by a cold, deleptonized star.