Gravitational shocks as a key ingredient of Gamma-Ray Bursts

TL;DR

This paper proposes a new mechanism involving gravitational shocks triggered by radial perturbations in neutron cores during supernovae, potentially explaining the energy release in gamma-ray bursts and their rarity.

Contribution

It introduces a novel physical process of gravitational shocks in near-critical collapse as a source of gamma-ray bursts, supported by numerical simulations.

Findings

Gravitational shocks can eject ultra-relativistic material during supernova collapse.

The mechanism's rarity aligns with observed gamma-ray burst frequency.

Near-critical collapse may also influence Active Galactic Nuclei activity.

Abstract

We identify a novel physical mechanism that may be responsible for energy release in $\gamma$-ray bursts. Radial perturbations in the neutron core, induced by its collision with collapsing outer layers during the early stages of supernova explosions, can trigger a gravitational shock, which can readily eject a small but significant fraction of the collapsing material at ultra-relativistic speeds. The development of such shocks is a strong-field effect arising in near-critical collapse in General Relativity and has been observed in numerical simulations in various contexts, including in particular radially perturbed neutron star collapse, albeit for a tiny range of initial conditions. Therefore, this effect can be easily missed in numerical simulations if the relevant parameter space is not exhaustively investigated. In the proposed picture, the observed rarity of $\gamma$-ray bursts would be explained if the relevant conditions for this mechanism appear in only about one in every $10^4-10^5$ core collapse supernovae. We also mention the possibility that near-critical collapse could play a role in powering the central engines of Active Galactic Nuclei.