Delayed neutrino-driven supernova explosions aided by the standing accretion-shock instability

TL;DR

This study uses 2D hydrodynamic simulations to demonstrate that the standing accretion-shock instability (SASI) significantly aids delayed neutrino-driven supernova explosions across a wider range of progenitors, emphasizing the role of shock oscillations.

Contribution

It provides detailed simulation evidence that SASI enhances shock revival and explosion timing in neutrino-driven supernova models, highlighting the effects of the nuclear equation of state and rotation.

Findings

SASI promotes shock expansion and explosion onset at about 600 ms post bounce.

A softer nuclear equation of state favors supernova explosions.

Rotation tends to suppress explosion likelihood by reducing neutrino heating.

Abstract

We present results of 2D hydrodynamic simulations of stellar core collapse, which confirm that the neutrino-heating mechanism remains viable for the explosion of a wider mass range of supernova progenitors with iron cores. We used an energy-dependent treatment of the neutrino transport based on the "ray-by-ray plus" approximation, in which the number, energy, and momentum equations are closed with a variable Eddington factor obtained by iteratively solving a model Boltzmann equation. We focus on the evolution of a 15 Msun progenitor and show that shock revival and the explosion are initiated at about 600 ms post bounce, powered by neutrino energy deposition. Similar to previous findings for an 11.2 Msun star, but significantly later, the onset of the explosion is fostered by the standing accretion shock instability (SASI). This instability exhibits highest growth rates for the dipole and quadrupole modes, which lead to large-amplitude bipolar shock oscillations and push the shock to larger radii, thus increasing the time accreted matter is exposed to neutrino heating in the gain layer. Therefore also convective overturn behind the shock is strengthened. A "soft" nuclear equation of state that causes a rapid contraction and a smaller radius of the forming neutron star and thus a fast release of gravitational binding energy, seems to be more favorable for an explosion. Rotation has the opposite effect because it leads to a more extended and cooler neutron star and thus lower neutrino luminosities and mean energies and overall less neutrino heating. Neutron star g-mode oscillations and the acoustic mechanism play no important role in our simulations. (abridged)