Nucleosynthesis in Outflows from Black Hole-Neutron Star Merger Disks With Full GR$\nu$RMHD

TL;DR

This paper uses advanced simulations to study the outflows from black hole-neutron star merger disks, showing they can produce conditions suitable for r-process nucleosynthesis and influence kilonova observations.

Contribution

The study presents the first full GR neutrino-radiation magnetohydrodynamics simulations of black hole-neutron star merger disks, revealing their potential for r-process element production.

Findings

Outflows are near the threshold for robust r-process nucleosynthesis.

Lanthanide fraction in outflows is lower than solar pattern.

Results suggest combined kilonova with blue and red components.

Abstract

Along with binary neutron star mergers, the in-spiral and merger of a black hole and a neutron star is a predicted site of $r$-process nucleosynthesis and associated kilonovae. For the right mass ratio, very large amounts of neutron rich material may become unbound from the post-merger accretion disk. We simulate a suite of four post-merger disks with full-transport general relativistic neutrino radiation magnetohydrodynamics. We find that the outflows from these disks are very close to the threshold conditions for robust $r$-process nucleosynthesis. For these conditions, the detailed properties of the outflow determine whether a full $r$-process can or cannot occur, implying that a wide range of observable phenomena are possible. We show that on average the disk outflow lanthanide fraction is suppressed relative to the solar isotopic pattern. In combination with the dynamical ejecta, these outflows imply a kilonova with both blue and red components.