Numerical Relativity Estimates of the Remnant Recoil Velocity in Binary Neutron Star Mergers

TL;DR

This paper estimates the recoil velocities of binary neutron star merger remnants using numerical relativity simulations, revealing velocities up to 150 km/s influenced by gravitational waves and matter ejection.

Contribution

It provides the first estimates of recoil velocities in neutron star mergers and offers fitting formulas relating recoil to ejected matter, aiding observational constraints.

Findings

Recoil velocities reach up to 150 km/s.

Remnant masses range from 2.34 to 3.38 solar masses.

Remnant spins are between 0.63 and 0.82.

Abstract

We present, for the first time, recoil velocity estimates for binary neutron star mergers using data from numerical relativity simulations. We find that binary neutron star merger remnants can have recoil velocity of the order of a few tens of km/s and as high as $150$ km/s in our dataset. These recoils are attained due to equivalent contributions from the anisotropic gravitational wave emission as well as the asymmetric ejection of dynamical matter during the merger. We provide fits for net recoil velocity as well as its ejecta component as a function of the amount of ejected matter, which may be useful when constraints on the ejected matter are obtained through electromagnetic observations. We also estimate the mass and spin of the remnants and find them to be in the range $[2.34, 3.38] M_{\odot}$ and $[0.63, 0.82]$ respectively, for our dataset.