Protoneutron Star Convection Simulated with a New General Relativistic Boltzmann Neutrino Radiation-Hydrodynamics Code

TL;DR

This study uses a new general relativistic Boltzmann neutrino radiation-hydrodynamics code to simulate convection in a protoneutron star, revealing sustained convection, increased neutrino emissions, and potential fast flavor conversions.

Contribution

It introduces a novel simulation code and provides the first 2D analysis of PNS convection with detailed neutrino transport and flavor conversion insights.

Findings

Convection is initiated and sustained in the 2D PNS simulation.

Convection enhances neutrino luminosities and energies.

Fast flavor conversion is likely in low $Y_e$ regions with high growth rates.

Abstract

We investigate the protoneutron star (PNS) convection using our newly developed general relativistic Boltzmann neutrino radiation-hydrodynamics code. This is a pilot study for more comprehensive investigations later. As such, we take a snapshot of a PNS at 2.3 seconds after bounce from a 1D PNS cooling calculation and run our simulation for $\sim160\,\mathrm{ms}$ in 2D under axisymmetry. The original PNS cooling calculation neglected convection entirely and the initial condition is linearly unstable to convection. We find in our 2D simulation that convection is instigated there indeed and expands inward after being full-fledged. The convection is then settled to a quasi-steady state in $\sim100\,\mathrm{ms}$, being sustained by the negative $Y_e$ gradient, which is in turn maintained by neutrino emissions. It enhances the luminosities and mean energies of all species of neutrinos compared to 1D. Taking advantage of the Boltzmann solver, we analyze the possible occurrence of the neutrino fast flavor conversion (FFC). We found that FFC is likely to occur in the regions, where $Y_e$ is lower, and that the growth rate can be as high as $\sim 10^{-1}\,{\mathrm{cm}^{-1}}$.