Total r-process Yields of Milky Way Neutron Star Mergers

Abstract

While it is now known that the mergers of double neutron star binary systems (NSMs) 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 NSMs hold sway over estimating their total contribution to the elemental abundances in the solar system and the Galaxy. Furthermore, the expected elemental yields of NSMs may depend on the merger parameters themselves—such as their stellar masses and radii—which are not currently considered in many galactic chemical evolution models. Using the characteristics of the observed sample of double neutron star (DNS) systems 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 solar system elements. We find that with our current models, the present DNS population favors the production of 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.