Total r-process Yields of Milky Way Neutron Star Mergers

TL;DR

This paper models the total r-process element yields from Milky Way neutron star mergers, comparing predictions with Solar system abundances to assess their role in heavy element production.

Contribution

It introduces a method to estimate nucleosynthetic yields from DNSs based on observed properties and compares these to Solar abundances, highlighting potential gaps in current models.

Findings

DNSs favor production of lighter r-process elements

Current models underproduce the heaviest elements

Additional sites or different DNS populations may be needed

Abstract

While it is now known that double neutron star binary systems (DNSs) are copious producers of heavy elements, there remains much speculation about whether they are the sole or even principal site of rapid neutron-capture (r-process) nucleosynthesis, one of the primary ways in which heavy elements are produced. The occurrence rates, delay times, and galactic environments of DNSs hold sway over estimating their total contribution to the elemental abundances in the Solar system and the Galaxy. Furthermore, the expected elemental yield for DNSs may depend on the merger parameters themselves -- such as their stellar masses and radii -- which is not currently considered in many galactic chemical evolution models. Using the characteristics of the observed sample of DNSs in the Milky Way as a guide, we predict the expected nucleosynthetic yields that a population of DNSs would produce upon merger, and we compare that nucleosynthetic signature to the heavy-element abundance pattern of the Solar system elements. We find that with our current models, the present DNS population favors production of the lighter r-process elements, while underproducing the heaviest elements relative to the Solar system. This inconsistency could imply an additional site for the heaviest elements or a population of DNSs much different from that observed today.