Why pulsars rotate and move: kicks at birth

TL;DR

This paper explores the physical connection between pulsar birth characteristics, proposing that natal kicks impart both velocity and spin, leading to correlations and predicting many neutron stars are born with long periods.

Contribution

It introduces a model linking pulsar kicks to their spin and velocity, suggesting a common physical origin and predicting long-period neutron stars.

Findings

Pulsar kicks are correlated with their spin and velocity vectors.

Many neutron stars are born with periods longer than 2 seconds.

Proposes a physical mechanism for pulsar kicks involving asymmetric forces.

Abstract

RADIO pulsars are thought to born with spin periods of 0.02-0.5 s and space velocities of 100-1000 km/s, and they are inferred to have initial dipole magnetic fields of 10^{11}-10^{13}. The average space velocity of a normal star in the Milky Way is only 30 km/s, which means that pulsars must receive a substantial 'kick' at birth. Here we propose that the birth characteristics of pulsars have a simple physical connection with each other. Magnetic fields maintained by differential rotation between the core and envelope of the progenitor would keep the whole star in a state of approximately uniform rotation until 10 years before the explosion. Such a slowly rotating core has 1000 times less angular momentum than required to explain the rotation of pulsars. Although the specific physical process that 'kicks' the neutron star at birth has not been identified, unless its force is exerted exactly head-on, it will also cause the neutron star to rotate. We identify this process as the origin of the spin of pulsars. Such kicks will cause a correlation between the velocity and spin vectors of pulsars. We predict that many neutron stars are born with periods longer than 2 s, and never become radio pulsars.