Turbulence in Magnetised Neutron Stars

TL;DR

This study uses high-resolution, long-duration simulations to investigate turbulence in magnetised neutron stars, revealing a turbulent cascade, helicity dynamics, and oscillation modes linked to observed magnetar phenomena.

Contribution

It presents the highest resolution and longest simulations to date, demonstrating turbulence effects and magnetic field behavior in neutron stars.

Findings

Evidence of a turbulent cascade absent in unmagnetised stars

Inverse helicity cascade leading to vanishing net helicity

Detection of a 145 Hz quadrupolar oscillation linked to Alfvenic modes

Abstract

The magnetic field configuration in the interior of neutron stars and its stability are open problems and may be impacted by the influence of a turbulent cascade within the star. Assessing the impact of turbulent flow with numerical simulations requires incredibly high resolution as well as long lived simulations covering multiple Alfven times. We present a series of simulations of magnetised neutron stars with resolution up to 29m and lasting at their longest 1.2s to assess this issue, the longest lasting and highest resolution such simulations to date. At the highest resolution we find evidence for a turbulent cascade absent in an unmagnetised star which cannot be captured with lower resolution simulations, consistent with Kolmogorov power law scaling. The presence of turbulence triggers an inverse cascade of helicity, while at late times the net helicity appears to vanish, suggesting that a twisted-torus is not formed in the magnetic field. We find that the presence of the magnetic field excites a characteristic quadrupolar oscillation of the density profile at 145 Hz, consistent with Alfvenic modes proposed as the source of quasi-periodic oscillations observed in magnetars.