Failure of a neutrino-driven explosion after core-collapse may lead to a thermonuclear supernova

TL;DR

This paper shows that under certain conditions, a thermonuclear explosion can occur in the outer shells of a collapsing star after a failed neutrino-driven supernova, potentially leading to a different type of supernova event.

Contribution

It demonstrates, through 1D simulations, that core-collapse can trigger thermonuclear explosions in outer stellar shells, a novel mechanism not previously confirmed.

Findings

Thermonuclear explosions can occur 10 seconds after core-collapse in certain conditions.

The explosions can unbind outer stellar layers, producing a supernova-like event.

The energy released is modest, less than 10^50 erg, with minimal nucleosynthesis.

Abstract

We demonstrate that $\sim10\,\textrm{s}$ after the core-collapse of a massive star, a thermonuclear explosion of the outer shells is possible for some (tuned) initial density and composition profiles, assuming that the neutrinos failed to explode the star. The explosion may lead to a successful supernova, as first suggested by Burbidge et al. We perform a series of one-dimensional (1D) calculations of collapsing massive stars with simplified initial density profiles (similar to the results of stellar evolution calculations) and various compositions (not similar to 1D stellar evolution calculations). We assume that the neutrinos escaped with a negligible effect on the outer layers, which inevitably collapse. As the shells collapse, they compress and heat up adiabatically, enhancing the rate of thermonuclear burning. In some cases, where significant shells of mixed helium and oxygen are present with pre-collapsed burning times of $\lesssim100\,\textrm{s}$ ($\approx10$ times the free-fall time), a thermonuclear detonation wave is ignited, which unbinds the outer layers of the star, leading to a supernova. The energy released is small, $\lesssim10^{50}\,\textrm{erg}$, and negligible amounts of synthesized material (including $^{56}$Ni) are ejected, implying that these 1D simulations are unlikely to represent typical core-collapse supernovae. However, they do serve as a proof of concept that the core-collapse-induced thermonuclear explosions are possible, and more realistic two-dimensional and three-dimensional simulations are within current computational capabilities.