Implosion-explosion in supernovae

TL;DR

This paper proposes an alternative model for supernova explosions, suggesting simultaneous inward and outward motions during early instability, challenging the traditional two-step core collapse and bounce scenario.

Contribution

It introduces a fluid mechanics-based model showing simultaneous inward and outward motions, and analyzes nonlinear regimes and shock formation in supernovae.

Findings

Identification of a saddle-center bifurcation in supernova dynamics.

Self-similar behavior in the nonlinear core collapse.

Revised understanding of remnant expansion as shock formation.

Abstract

Supernovae explosions of massive stars are nowadays believed to result from a two-step process, with an initial gravitational core collapse followed by an expansion of matter after a bouncing on the core. This scenario meets several difficulties. We show that it is not the only possible one: a simple model based on fluid mechanics and stability properties of the equilibrium state shows that one can have also a simultaneous inward/outward motion in the early stage of the instability of the supernova. This shows up in the slow sweeping across a saddle-center bifurcation found when considering equilibrium states associated to the constraint of energy conservation. We first discuss the weakly nonlinear regime in terms of a Painlev\'e I equation. We then show that the strongly nonlinear regime displays a self-similar behavior of the core collapse. Finally, the expansion of the remnants is revisited as an isentropic process leading to shocks formation.