The mass ejection from the merger of binary neutron stars

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.