On the astrophysical robustness of neutron star merger r-process

TL;DR

This study demonstrates that neutron star mergers produce a highly robust and consistent r-process nucleosynthesis pattern across various system parameters, confirming their role as primary sources of heavy elements in the universe.

Contribution

It provides a systematic analysis showing the robustness of r-process yields in neutron star mergers, highlighting their insensitivity to system parameters and nuclear physics.

Findings

All studied binary systems produce similar abundance patterns.

The r-process occurs along the neutron drip line, driven mainly by nuclear properties.

Neutron star mergers are confirmed as major sources of cosmic heavy r-process elements.

Abstract

In this study we explore the nucleosynthesis in the dynamic ejecta of compact binary mergers. We are particularly interested in the question how sensitive the resulting abundance patterns are to the parameters of the merging system. Therefore, we systematically investigate combinations of neutron star masses in the range from 1.0 to 2.0 \Msun and, for completeness, we compare the results with those from two simulations of a neutron star black hole merger. The ejecta masses vary by a factor of five for the studied systems, but all amounts are (within the uncertainties of the merger rates) compatible with being a major source of cosmic r-process. The ejecta undergo a robust r-process nucleosynthesis which produces all the elements from the second to the third peak in close-to-solar ratios. Most strikingly, this r-process is extremely robust, all 23 investigated binary systems yield practically identical abundance patterns. This is mainly the result of the ejecta being extremely neutron rich (\ye $\approx0.04$) and the r-process path meandering along the neutron drip line so that the abundances are determined entirely by nuclear rather than by astrophysical properties. This robustness together with the ease with which both the second and third peak are reproduced make compact binary mergers the prime candidate for the source of the observed unique heavy r-process component.