STELLAR CORE COLLAPSE - A BOLTZMANN TREATMENT OF NEUTRINO-ELECTRON SCATTERING

Neutrino-electron scattering plays a major role in the deleptonization of the iron core during the gravitational collapse of a presupernova star and, hence, plays a major role in the success or failure of the shock ejection mechanism for Type II supernovae. In this paper we present the first simulation of realistic gravitational collapse in which neutrino-electron scattering is not approximated in the neutrino transport equation with either a truncated Legendre series or a Fokker-Planck approximation. We begin with a 1.17 M. iron core extracted from a Nomoto-Hashimoto 13 M. presupernova star. Our simulation is carried out using a code that we developed that is based on the Newtonian gravity, O(v/c) Lagrangian hydrodynamics equations and the O(v/c) neutrino Boltzmann equation. Hence, our code computes the neutrino transport accurately. To simulate the nuclear physics, we couple our code to the Baron-Cooperstein equation of state. Because at present we are interested in the infall phase, we include only electron-neutrinos. In particular, we include the following weak interactions in the electron-neutrino Boltzmann equation: electron capture on nuclei and free protons, electron-neutrino absorption on nuclei and free neutrons, conservative scattering of electron-neutrinos on free protons and neutrons, conservative coherent scattering of electron-neutrinos on nuclei, and neutrino-electron scattering. The results of our simulation are presented together with the results from a simulation carried out with Bruenn's radiation-hydrodynamics code, which uses multigroup flux-limited diffusion for the neutrino transport, for the same initial model and equation of state. We discuss the differences in the results obtained with the two independent codes and their implications for the subsequent evolution.