2D Multi-Angle, Multi-Group Neutrino Radiation-Hydrodynamic Simulations of Postbounce Supernova Cores

TL;DR

This study uses advanced 2D multi-angle neutrino transport simulations to analyze postbounce supernova cores, revealing significant differences from traditional methods, especially in rotating models, impacting shock dynamics and neutrino heating.

Contribution

It introduces a genuinely 2D multi-angle neutrino transport method and compares its results with flux-limited diffusion, highlighting its advantages in capturing aspherical radiation fields.

Findings

Multi-angle transport predicts larger neutrino flux asymmetries in rotating models.

Enhanced neutrino heating by up to a factor of 3 along the poles.

Multi-angle calculations show up to 30% higher neutrino energy deposition at later times.

Abstract

We perform axisymmetric (2D) multi-angle, multi-group neutrino radiation-hydrodynamic calculations of the postbounce phase of core-collapse supernovae using a genuinely 2D discrete-ordinate (S_n) method. We follow the long-term postbounce evolution of the cores of one nonrotating and one rapidly-rotating 20-solar-mass stellar model for ~400 milliseconds from 160 ms to ~550 ms after bounce. We present a multi-D analysis of the multi-angle neutrino radiation fields and compare in detail with counterpart simulations carried out in the 2D multi-group flux-limited diffusion (MGFLD) approximation to neutrino transport. We find that 2D multi-angle transport is superior in capturing the global and local radiation-field variations associated with rotation-induced and SASI-induced aspherical hydrodynamic configurations. In the rotating model, multi-angle transport predicts much larger asymptotic neutrino flux asymmetries with pole to equator ratios of up to ~2.5, while MGFLD tends to sphericize the radiation fields already in the optically semi-transparent postshock regions. Along the poles, the multi-angle calculation predicts a dramatic enhancement of the neutrino heating by up to a factor of 3, which alters the postbounce evolution and results in greater polar shock radii and an earlier onset of the initially rotationally weakened SASI. In the nonrotating model, differences between multi-angle and MGFLD calculations remain small at early times when the postshock region does not depart significantly from spherical symmetry. At later times, however, the growing SASI leads to large-scale asymmetries and the multi-angle calculation predicts up to 30% higher average integral neutrino energy deposition rates than MGFLD.