Turbulence in magnetized neutron stars

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 magnetized neutron stars with resolutions up to 29 m and lasting at their longest 1.2 s 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 unmagnetized 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.