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 s hock ejection mechanism for Type II supernovae. In this paper we prese nt the first simulation of realistic gravitational collapse in which n eutrino-electron scattering is not approximated in the neutrino transp ort equation with either a truncated Legendre series or a Fokker-Planc k approximation. We begin with a 1.17 M. iron core extracted from a No moto-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 Bol tzmann equation. Hence, our code computes the neutrino transport accur ately. To simulate the nuclear physics, we couple our code to the Baro n-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, elect ron-neutrino absorption on nuclei and free neutrons, conservative scat tering of electron-neutrinos on free protons and neutrons, conservativ e coherent scattering of electron-neutrinos on nuclei, and neutrino-el ectron scattering. The results of our simulation are presented togethe r with the results from a simulation carried out with Bruenn's radiati on-hydrodynamics code, which uses multigroup flux-limited diffusion fo r the neutrino transport, for the same initial model and equation of s tate. We discuss the differences in the results obtained with the two independent codes and their implications for the subsequent evolution.