The r-Process: History, Required Conditions, Astrophysical Sites, and Observations

TL;DR

This review discusses the history, conditions, astrophysical sites, and observations related to the r-process, emphasizing the comparison between models and stellar observations to identify astrophysical sources.

Contribution

It provides a comprehensive overview of the r-process, integrating nuclear physics, astrophysical site proposals, and observational data to advance understanding of heavy element synthesis.

Findings

Solar r-abundance pattern can be reconstructed by subtracting s-process contributions.

Current models struggle to definitively identify the astrophysical sites of the r-process.

Observations of low-metallicity stars provide clues to early Galaxy r-process contributions.

Abstract

This review of the rapid-neutron-capture (i.e. r-) process starts with determining the Solar System r-abundance pattern via first obtaining (and subtracting) the contribution from the slow-neutron capture (s-) process. We emphasize the extensive work in this area by our late colleague Roberto Gallino and continue in an overview, concentrating on attempts to reproduce the solar r-process pattern with historical site-independent approaches, based on nuclear physics far from stability. In a second step we address the existing proposals for astrophysical sites. Among stellar observations we start with available observations of individual events before analyzing low-metallicity stars, which witness r-process contributions in the early Galaxy. We conclude with a comparison of observations and model predictions, focusing on our present ability to identify the responsible individual astrophysical sites by their imprint in Galactic evolution.