r-Process Nucleosynthesis in Shocked Surface Layers of O-Ne-Mg Cores

TL;DR

This paper proposes that rapid expansion of shocked surface layers in O-Ne-Mg cores during supernovae can produce heavy r-process isotopes, potentially explaining their abundance in the galaxy.

Contribution

It introduces a new mechanism for r-process nucleosynthesis occurring in the shocked surface layers of collapsing O-Ne-Mg cores.

Findings

Heavy r-process isotopes can form despite low neutron excess.

The yields may account for the Galactic inventory of these isotopes.

Rapid expansion maintains disequilibrium, enabling nucleosynthesis.

Abstract

We demonstrate that rapid expansion of the shocked surface layers of an O-Ne-Mg core following its collapse can result in r-process nucleosynthesis. As the supernova shock accelerates through these layers, it makes them expand so rapidly that free nucleons remain in disequilibrium with alpha-particles throughout most of the expansion. This allows heavy r-process isotopes including the actinides to form in spite of the very low initial neutron excess of the matter. We estimate that yields of heavy r-process nuclei from this site may be sufficient to explain the Galactic inventory of these isotopes.