Can neutron star mergers alone explain the r-process enrichment of the Milky Way?

Chiaki Kobayashi, Ilya Mandel, Krzysztof Belczynski, Stephane Goriely, Thomas H. Janka, Oliver Just, Ashley J. Ruiter, Dany Van Beveren, Matthias U. Kruckow, Max M. Briel, Jan J. Eldridge, Elizabeth Stanway

Published 2022-11-08Version 1

Comparing Galactic chemical evolution models to the observed elemental abundances in the Milky Way, we show that neutron star mergers can be a leading r-process site only if such mergers have very short delay times and/or beneficial masses of the compact objects at low metallicities. Namely, black hole-neutron star mergers, depending on the black-hole spins, can play an important role in the early chemical enrichment of the Milky Way. We also show that none of the binary population synthesis models used in this paper, i.e., COMPAS, StarTrack, Brussels, ComBinE, and BPASS, can currently reproduce the elemental abundance observations. The predictions are problematic not only for neutron star mergers, but also for Type Ia supernovae, which may point to shortcomings in binary evolution models.