Kicks and Induced Spins of Neutron Stars at Birth

TL;DR

This paper uses simulations to study how supernova explosions impart kicks and spins to neutron stars, revealing the significant role of neutrino emissions and their implications for pulsar velocities and spin orientations.

Contribution

It demonstrates that neutrino recoil can dominate neutron star kicks, and explores the relationship between induced spins and kicks, providing new insights into pulsar birth properties.

Findings

Neutrino recoil can be as large or larger than matter recoil in neutron star kicks.

The sign of neutrino momentum can oppose matter recoil, affecting pulsar motion.

Induced spins are comparable to observed pulsar spins and may anti-correlate with kick directions.

Abstract

Using simulations of non-rotating supernova progenitors, we explore the kicks imparted to and the spins induced in the compact objects birthed in core collapse. We find that the recoil due to neutrino emissions can be a factor affecting core recoil, comparable to and at times larger than the corresponding kick due to matter recoil. This result would necessitate a revision of the general model of the origin of pulsar proper motions. In addition, we find that the sign of the net neutrino momentum can be opposite to the sign of the corresponding matter recoil. As a result, at times the pulsar recoil and ejecta can be in the same direction. Moreover, our results suggest that the duration of the dipole in the neutrino emissions can be shorter than the duration of the radiation of the neutron-star binding energy. This allows a larger dipole asymmetry to arise, but for a shorter time, resulting in kicks in the observed pulsar range. Furthermore, we find that the spin induced by the aspherical accretion of matter can leave the residues of collapse with spin periods comparable to those inferred for radio pulsars and that there seems to be a slight anti-correlation between the direction of the induced spin and the net kick direction. This could explain such a correlation among observed radio pulsars. Finally, we find that the kicks imparted to black holes are due to the neutrino recoil alone, resulting in birth kicks $\le$100 km s$^{-1}$ most of the time.