Nonequilibrium Neutronization and Large-Scale Convection in Gravitational Collapse

Abstract

Most of the energy released by the gravitational collapse of the cores of massive stars is carried away by neutrinos. The self-consistent problem of gravitational collapse is solved using 2D gas dynamics considering the spectral transport of neutrinos in the flux-limited diffusion. It is shown that large-scale convection develops in the region near the neutrinosphere and leads to an increase in the average neutrino energy up to 15–18 MeV, which is 1.5 times higher than the results of 1D calculations. This study improves a simple model of neutronization in the central opaque region, which is applicable, strictly speaking, only in the transparent region. The 2D model correctly reproduces the high chemical potential of degenerate electrons ~60 MeV at the center with a high density of matter, as in spherically symmetric calculations with exact account of the weak interaction. Since neutronization at the center is reversible due to trapped neutrinos, the instability development in the center is suppressed, and the high chemical potential of electrons at the center in the refined neutronization model does not affect the energy of outgoing neutrinos. The obtained neutrino energies are important both for explaining the supernova phenomenon and for setting up an experiment to detect neutrinos from a supernova.