The relative contribution to heavy metals production from binary neutron star mergers and neutron star-black hole mergers

Abstract

The origin of the heavy elements in the Universe is not fully determined. Neutron star-black hole (NSBH) and {binary neutron star} (BNS) mergers may both produce heavy elements via rapid neutron-capture (r-process). We use the recent detection of gravitational waves from NSBHs, improved measurements of the neutron star equation-of-state, and the most modern numerical simulations of ejected material from binary collisions to measure the relative contribution of NSBHs and BNSs to the production of heavy elements. As the amount of r-process ejecta depends on the mass and spin distribution of the compact objects, as well as on the equation-of-state of the neutron stars, we consider various models for these quantities, informed by gravitational-wave and pulsar data. We find that in most scenarios, BNSs have produced more r-process elements than NSBHs over the past 2.5 billion years. If black holes have preferentially small spins, BNSs can produce at least twice of the amount of r-process elements than NSBHs. If black hole spins are small and there is a dearth of low mass ($<5M_{\odot }$) black holes within NSBH binaries, BNSs can account for the near totality of the r-process elements from binaries. For NSBH to produce large fraction of r-process elements, black holes in NSBHs must have small masses and large aligned spins, which is disfavored by current data.

Accepted version by The Astrophysical Journal Letters

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• GRMHD simulations of neutron-star mergers with weak interactions: r-process nucleosynthesis and electromagnetic signatures of dynamical ejecta
• Population properties and multimessenger prospects of neutron star-black hole mergers following GWTC-3
• A study of the agreement between binary neutron star ejecta models derived from numerical relativity simulations
• Nucleosynthesis in outflows of compact objects and detection prospects of associated kilonovae
• Population properties of neutron stars in the coalescing compact binaries
• Inference of multi-channel r-process element enrichment in the Milky Way using binary neutron star merger observations
• R-process beta-decay neutrino flux from binary neutron star mergers and collapsars