Mass Ejection in Failed Supernovae: Variation with Stellar Progenitor

TL;DR

This study investigates how different stellar progenitors eject mass during failed supernovae, revealing that the amount and energy of ejected mass depend on stellar type and core properties, with implications for observable shock breakout signals.

Contribution

It introduces a parametric, spherically-symmetric hydrodynamic model to analyze mass ejection mechanisms across various stellar progenitors in failed supernovae.

Findings

Mass ejection varies with stellar type, from several solar masses to less than 0.001 solar masses.

Final shock energy decreases with core-compactness, remaining below 10^{48} erg.

Successful ejection depends on envelope mass, core-compactness, and can involve fallback accretion.

Abstract

We study the ejection of mass during stellar core-collapse when the stalled shock does not revive and a black hole forms. Neutrino emission during the protoneutron star phase causes a decrease in the gravitational mass of the core, resulting in an outward going sound pulse that steepens into a shock as it travels out through the star. We explore the properties of this mass ejection mechanism over a range of stellar progenitors using spherically-symmetric, time-dependent hydrodynamic simulations that treat neutrino mass loss parametrically and follow the shock propagation over the entire star. We find that all types of stellar progenitor can eject mass through this mechanism. The ejected mass is a decreasing function of the surface gravity of the star, ranging from several $M_\odot$ for red supergiants to $\sim 0.1M_\odot$ for blue supergiants and $\sim 10^{-3} M_\odot $ for Wolf-Rayet stars. We find that the final shock energy at the surface is a decreasing function of the core-compactness, and is $\lesssim 10^{47}-10^{48}$ erg in all cases. In progenitors with a sufficiently large envelope, high core-compactness, or a combination of both, the sound pulse fails to unbind mass. Successful mass ejection is accompanied by significant fallback accretion that can last from hours to years. We predict the properties of shock breakout and thermal plateau emission produced by the ejection of the outer envelope of blue supergiant and Wolf-Rayet progenitors in otherwise failed supernovae.