Metallicity-Suppressed Collapsars Cannot be the Dominant r-Process Source in the Milky Way

TL;DR

This study uses an advanced analytical model of Galactic Chemical Evolution to evaluate potential r-process sources, concluding that neutron star mergers, not collapsars, are the primary contributors to the Milky Way's r-process element enrichment.

Contribution

It introduces a high-dimensional analytical model that tests the viability of collapsars versus neutron star mergers as r-process sources, ruling out collapsars as dominant in the Milky Way.

Findings

Neutron star mergers can account for most r-process material.

Models with dominant collapsar yields are inconsistent with observational data.

The analysis constrains the possible sources of r-process elements in the galaxy.

Abstract

We develop a high-performance analytical model of Galactic Chemical Evolution, which accounts for delay time distributions and lock-up of stellar yields in a thermal-phased ISM. The model is capable of searching, for the first time, through the high-dimensional parameter space associated with the r-process enrichment of the Milky Way by its possible sources: Neutron Star Mergers and Collapsar events. Their differing formation mechanisms give these two processes different time dependencies, a property which has frequently been used to argue in favour of collapsars as the dominant r-process source. However, we show that even with large degrees of freedom in the allowed thermal, structural, and chemical properties of the galaxy, large regions of parameter space are in strong tension with the data. In particular, whilst we are able to find models in which neutron star mergers produce the majority of r-process material, the data rule out all models with dominant collapsar yields. With no other identified source, we conclude that Neutron Star Mergers must be the dominant contributors to the modern Milky Way r-process budget.