Theoretical Support for the Hydrodynamic Mechanism of Pulsar Kicks

TL;DR

This paper presents a two-dimensional simulation demonstrating that hydrodynamic processes during core-collapse supernovae can naturally produce neutron star kicks with velocities comparable to observed values, primarily driven by asymmetric ejecta.

Contribution

It provides the first detailed simulation showing hydrodynamically driven neutron star kicks with realistic velocities, emphasizing the role of anisotropic ejecta over neutrino emission.

Findings

Neutron star achieved ~150 km/s velocity in simulation.

Recoil mainly caused by asymmetric ejecta, neutrino contribution <2%.

Simulation supports hydrodynamic mechanism as a natural explanation for observed pulsar kicks.

Abstract

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 (NS) via an induced, neutrino-driven explosion. During the explosion, a ~10% anisotropy in the low-mass, high-velocity ejecta lead to recoil of the high-mass neutron star. At the end of our simulation, the NS 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, non-exotic mechanism with which to obtain neutron star kicks.