  The LIGO-Virgo gravitational wave detectors have confidently observed 4
events involving neutron stars: two binary neutron star (BNS) mergers (GW170817
and GW190425), and two neutron star-black hole mergers (GW200105 and GW200115).
However, our theoretical understanding of the remnant properties of such
systems is incomplete due to the complexities related to the modeling of matter
effects and the very high computational cost of corresponding numerical
relativity simulations. An important such property is the recoil velocity,
which is imparted onto the remnant due to the anisotropic emission of
gravitational radiation and the dynamical ejection of matter in the kilonova.
In this work, we combine gravitational radiation as well as dynamical ejecta
distributions, computed by the Computational Relativity numerical simulations,
to get accurate estimates for BNS remnant recoil velocities. We find that
recoils due to ejection of matter dominate those caused by gravitational wave
emission. Knowledge of BNS remnant recoil velocities is important in
determining if the remnant is retained by its environment for future
hierarchical mergers which, in turn, can form binaries with black holes in the
so-called lower mass gap of 3 to 5 solar masses.
