R-Process elements from magnetorotational hypernovae

TL;DR

This paper presents evidence that magnetorotational hypernovae in the early universe contributed significantly to r-process element production, explaining observed abundance patterns in extremely metal-poor stars.

Contribution

It identifies magnetorotational hypernovae as a new site of r-process nucleosynthesis, expanding understanding beyond neutron-star mergers.

Findings

The star SMSS J200322.54-114203.3 shows a large r-process element enhancement.

The observed abundance pattern matches yields from a 25-solar-mass hypernova.

Hypernovae could produce both r-process and light elements in early star formation epochs.

Abstract

Neutron-star mergers were recently confirmed as sites of rapid-neutron-capture (r-process) nucleosynthesis. However, in Galactic chemical evolution models, neutron-star mergers alone cannot reproduce the observed element abundance patterns of extremely metal-poor stars, which indicates the existence of other sites of r-process nucleosynthesis. These sites may be investigated by studying the element abundance patterns of chemically primitive stars in the halo of the Milky Way, because these objects retain the nucleosynthetic signatures of the earliest generation of stars. Here we report the element abundance pattern of the extremely metal-poor star SMSS J200322.54-114203.3. We observe a large enhancement in r-process elements, with very low overall metallicity. The element abundance pattern is well matched by the yields of a single 25-solar-mass magnetorotational hypernova. Such a hypernova could produce not only the r-process elements, but also light elements during stellar evolution, and iron-peak elements during explosive nuclear burning. Hypernovae are often associated with long-duration gamma-ray bursts in the nearby Universe. This connection indicates that similar explosions of fast-spinning strongly magnetized stars occurred during the earliest epochs of star formation in our Galaxy.