From Nuclei to the Cosmos: Tracing Heavy-Element Production with the Oldest Stars

TL;DR

This paper reviews how ancient stars in the Milky Way and dwarf galaxies serve as cosmic archives, revealing the origins of heavy elements through neutron-capture processes and recent discoveries like the r-process galaxy Reticulum II.

Contribution

It highlights the use of old stars to identify astrophysical sites of heavy-element synthesis, especially neutron star mergers, advancing understanding of nucleosynthesis history.

Findings

Old stars preserve elemental patterns from 13 billion years ago.

Reticulum II galaxy shows evidence of neutron star merger enrichment.

Old dwarf galaxies help constrain r-process astrophysical sites.

Abstract

Understanding the origin of the elements has been a decades long pursuit, with many open questions still remaining. Old stars found in the Milky Way and its dwarf satellite galaxies can provide answers because they preserve clean elemental patterns of the nucleosynthesis processes that operated some 13 billion years ago. This enables the reconstruction of the chemical evolution of the elements. Here we focus on the astrophysical signatures of heavy neutron-capture elements made in the s-, i- and r-process found in old stars. A highlight is the recently discovered r-process galaxy Reticulum II that was apparently enriched by a neutron star merger. These results show that old stars in dwarf galaxies provide a novel means to constrain the astrophysical site of the r-process, ushering in much needed progress on this major outstanding question. This nuclear astrophysics work complements the many nuclear physics efforts into heavy-element formation, and aligns with recent results on the gravitational wave signature of a neutron star merger.