Binary Neutron Star Mergers: Mass Ejection, Electromagnetic Counterparts and Nucleosynthesis

TL;DR

This study uses numerical relativity to analyze mass ejection, electromagnetic signals, and nucleosynthesis in binary neutron star mergers, revealing how these phenomena depend on binary parameters and the neutron star equation of state.

Contribution

It provides a comprehensive simulation-based analysis of mass ejection, electromagnetic transients, and nucleosynthesis, highlighting the dependence on binary parameters and the neutron star EOS.

Findings

A few 10^{-3} solar masses of material are ejected during mergers.

Bright radio flares can result from shock-accelerated ejecta, observable weeks to years after merger.

Kilonova light curves depend on merger outcomes and can constrain the neutron star EOS.

Abstract

We present a systematic numerical relativity study of the mass ejection and the associated electromagnetic transients and nucleosynthesis from binary neutron star (NS) mergers. We find that a few $10^{-3}\, M_\odot$ of material are ejected dynamically during the mergers. The amount and the properties of these outflow depend on binary parameters and on the NS equation of state (EOS). A small fraction of these ejecta, typically ${\sim}10^{-6}\, M_\odot$, is accelerated by shocks formed shortly after merger to velocities larger than $0.6\, {\rm c}$ and produces bright radio flares on timescales of weeks, months, or years after merger. Their observation could constrain the strength with which the NSs bounce after merger and, consequently, the EOS of matter at extreme densities. The dynamical ejecta robustly produce second and third $r$-process peak nuclei with relative isotopic abundances close to solar. The production of light $r$-process elements is instead sensitive to the binary mass ratio and the neutrino radiation treatment. Accretion disks of up to ${\sim}0.2\, M_\odot$ are formed after merger, depending on the lifetime of the remnant. In most cases, neutrino- and viscously-driven winds from these disks dominate the overall outflow. Finally, we generate synthetic kilonova light curves and find that kilonovae depend on the merger outcome and could be used to constrain the NS EOS.