Theoretical Support for the Hydrodynamic Mechanism of Pulsar Kicks

The collapse of a massive star’s core, followed by a neutrino-driven, asymmetric supernova explosion, can naturally lead to pulsar recoils and neutron star kicks. Here, we present a two-dimensional, radiation-hydrodynamic simulation in which core collapse leads to significant acceleration of a fully formed, nascent neutron star via an induced, neutrino-driven explosion. During the explosion, an ~10% anisotropy in the low-mass, high-velocity ejecta leads to recoil of the high-mass neutron star. At the end of our simulation, the neutron star has achieved a velocity of ~150 km s^(-1) and is accelerating at ~350 km s^(-2), but has yet to reach the ballistic regime. The recoil is due almost entirely to hydrodynamical processes, with anisotropic neutrino emission contributing less than 2% to the overall kick magnitude. Since the observed distribution of neutron star kick velocities peaks at ~300–400 km s^(-1), recoil due to anisotropic core-collapse supernovae provides a natural, nonexotic mechanism with which to obtain neutron star kicks.