Magnetorotational instability in proto-neutron stars

TL;DR

This paper investigates the stability of differentially rotating magnetized proto-neutron stars, deriving new MRI criteria that differ from standard conditions, and finds MRI growth is slow and localized near regions with specific magnetic field configurations.

Contribution

It derives novel MRI stability criteria for proto-neutron stars without assuming weak magnetic fields, revealing different conditions and growth behaviors than in standard models.

Findings

MRI occurs near regions with vanishing radial magnetic field component.

MRI growth rate is slow, especially for larger-scale perturbations.

MRI growth in proto-neutron stars is slower than the Goldreich-Schubert-Fricke instability.

Abstract

Magnetorotational instability (MRI) has been suggested to lead a rapid growth of the magnetic field in core collapse supernovae and produce departures from spherical syymmetry that can be important in determining the explosion mechanism. We address the problem of stability in differentially rotating magnetized proto-neutron stars at the beginning of their evolution. Criteria for MRI in proto-neutron stars are derived without simplying assumptions about a weak magnetic field and are substantially different from the standard condition. If the magnetic field is strong, MRI can occur only in the neighbourhood of the region where the spherical radial component of the magnetic field vanishes. The growth rate of MRI is relatively low except for perturbations with very small scales which usually are not detected in numerical simulations. We find that MRI in proto-neutron stars grows more slowly than than the double diffusive instability analogous the Goldreich-Schubert-Fricke instability in ordinary stars.