Neutron Star Mergers and Nucleosynthesis of Heavy Elements

TL;DR

This paper reviews neutron star mergers as key sites for heavy element nucleosynthesis, discussing observational evidence, nucleosynthesis processes, and modeling uncertainties, concluding they are likely the main source of r-process elements in the galaxy.

Contribution

It provides a comprehensive overview of neutron star mergers' role in heavy element formation, highlighting recent observational and theoretical developments and uncertainties.

Findings

Neutron star mergers are consistent with solar r-process abundances.

They are likely the dominant source of r-process nuclei in the galaxy.

Modeling uncertainties significantly affect nucleosynthesis predictions.

Abstract

The existence of neutron star mergers has been supported since the discovery of the binary pulsar and the observation of its orbital energy loss, consistent with General Relativity. They are considered nucleosynthesis sites of the rapid neutron-capture process (r-process), which is responsible for creating approximately half of all heavy elements beyond Fe and is the only source of elements beyond Pb and Bi. Detailed nucleosynthesis calculations based on the decompression of neutron star matter are consistent with solar r-process abundances of heavy nuclei. Neutron star mergers have also been identified with short-duration {\gamma}-ray bursts via their IR afterglow. The high neutron densities in ejected matter permit a violent r-process, leading to fission cycling of the heaviest nuclei in regions far from (nuclear) stability. Uncertainties in several nuclear properties affect the abundance distributions. The modeling of astrophysical events also depends on the hydrodynamic treatment, the occurrence of a neutrino wind after the merger and before the possible emergence of a black hole, and the properties of black hole accretion disks. We discuss the effect of nuclear and modeling uncertainties and conclude that binary compact mergers are probably a (or the) dominant site of the production of r-process nuclei in our Galaxy.