Nuclear fission reaction simulations in compact stars

TL;DR

This paper presents novel reaction network simulations of actinide-rich solids in cooling white dwarfs, revealing how neutron-capture and fission reactions could trigger thermonuclear explosions leading to Type-Ia supernovae.

Contribution

It introduces new simulation results showing how neutron-capture and fission in actinides can initiate supernova explosions in white dwarfs.

Findings

Neutron-capture on U-238 and Th-232 breeds fissile nuclei.

Significant fission of U and Th can occur during the chain-reaction.

Energy release from fission may ignite thermonuclear carbon burning.

Abstract

Type-Ia supernovae (SN Ia) are powerful stellar explosions that provide important distance indicators in cosmology. Recently, we proposed a new SN Ia mechanism that involves a nuclear fission chain-reaction in an isolated white dwarf [PRL 126, 1311010]. Here we perform novel reaction network simulations of the actinide-rich first solids in a cooling white dwarf. The network includes neutron-capture and fission reactions on a range of U and Th isotopes with various possible values for U-235 enrichment. We find, for modest U-235 enrichments, neutron-capture on U-238 and Th-232 can breed additional fissile nuclei so that a significant fraction of all U and Th nuclei may fission during the chain-reaction. The resulting large energy release could ignite thermonuclear carbon burning and possibly trigger a SN Ia.