Induced Rotation in 3D Simulations of Core Collapse Supernovae: Implications for Pulsar Spins

TL;DR

This study uses 3D simulations to investigate how turbulence and instabilities in supernovae can induce rotation in the resulting neutron stars, finding that significant spin-up is unlikely but modest rotation periods are possible.

Contribution

First 3D simulation of supernova core collapse showing turbulence-induced rotation effects on neutron star spin without initial core rotation.

Findings

No significant spin-up of proto-neutron star observed.

Strong differential rotation develops in the gain region.

Induced rotation periods are generally modest, around seconds.

Abstract

It has been suggested that the observed rotation periods of radio pulsars might be induced by a non-axisymmetric spiral-mode instability in the turbulent region behind the stalled supernova bounce shock, even if the progenitor core was not initially rotating. In this paper, using the three-dimensional AMR code CASTRO with a realistic progenitor and equation of state and a simple neutrino heating and cooling scheme, we present a numerical study of the evolution in 3D of the rotational profile of a supernova core from collapse, through bounce and shock stagnation, to delayed explosion. By the end of our simulation ($\sim$420 ms after core bounce), we do not witness significant spin up of the proto-neutron star core left behind. However, we do see the development before explosion of strong differential rotation in the turbulent gain region between the core and stalled shock. Shells in this region acquire high spin rates that reach $\sim$$150\,$ Hz, but this region contains too little mass and angular momentum to translate, even if left behind, into rapid rotation for the full neutron star. We find also that much of the induced angular momentum is likely to be ejected in the explosion, and moreover that even if the optimal amount of induced angular momentum is retained in the core, the resulting spin period is likely to be quite modest. Nevertheless, induced periods of seconds are possible.