The mass ejection from the merger of binary neutron stars

TL;DR

This study uses numerical-relativity simulations to analyze the properties of material ejected during binary neutron star mergers, revealing velocities, mass ranges, and potential electromagnetic signals depending on the equation of state and system parameters.

Contribution

It provides detailed predictions of ejecta velocities, masses, and energies, and explores their dependence on EOS and binary parameters, informing electromagnetic counterpart searches.

Findings

Ejected material has velocities up to 0.8c.

Ejected mass ranges from 10^{-4} to 10^{-2} solar masses.

Ejecta could produce observable electromagnetic signals.

Abstract

Numerical-relativity simulations for the merger of binary neutron stars are performed for a variety of equations of state (EOSs) and for a plausible range of the neutron-star mass, focusing primarily on the properties of the material ejected from the system. We find that a fraction of the material is ejected as a mildly relativistic and mildly anisotropic outflow with the typical and maximum velocities $\sim 0.15$ -- $0.25c$ and $\sim 0.5$ -- $0.8c$ (where $c$ is the speed of light), respectively, and that the total ejected rest mass is in a wide range $10^{-4}$ -- $10^{-2}M_{\odot}$, which depends strongly on the EOS, the total mass, and the mass ratio. The total kinetic energy ejected is also in a wide range between $10^{49}$ and $10^{51} {\rm ergs}$. The numerical results suggest that for a binary of canonical total mass $2.7M_{\odot}$, the outflow could generate an electromagnetic signal observable by the planned telescopes through the production of heavy-element unstable nuclei via the $r$-process or through the formation of blast waves during the interaction with the interstellar matter, if the EOS and mass of the binary are favorable ones.