Cascade Processes of Strong and Weak MHD Turbulence

TL;DR

This study investigates relativistic MHD turbulence through high-resolution simulations, revealing similarities and differences with non-relativistic turbulence, and applying findings to neutron star magnetospheres and pulsar X-ray emissions.

Contribution

It provides new insights into the properties of relativistic MHD turbulence, including spectral and anisotropic characteristics, and links these to astrophysical phenomena.

Findings

Power spectra and anisotropies resemble non-relativistic MHD turbulence.

Magnetic field intermittency is stronger in strong turbulence.

Generated Alfvén and fast modes exhibit distinct spectra and anisotropies.

Abstract

On the framework of relativistic force-free magnetohydrodynamic (MHD) turbulence, we explore the fundamental properties of strong and weak turbulent cascades using high-resolution numerical simulations in the presence of a uniform background magnetic field. We find that (1) power spectra and scale-dependent anisotropies both for the strong and weak turbulence resemble those observed in the non-relativistic MHD turbulence; (2) intermittency of magnetic fields in strong turbulence is stronger than that in the weak one; (3) generated Alfv\'en modes show similar energy spectra and scale-dependent anisotropies to those of non-relativistic case; (4) generated fast modes present a power spectrum similar to that of Alfv\'en modes, with a strong (for strong turbulence) or weak (for weak turbulence) scale-dependent anisotropy, which are significantly different from non-relativistic turbulence; and (5) applications of our numerical results to neutron star magnetospheres show that the strong (or moderately weak) turbulent cascade can explain the X-ray radiation of the Vela pulsar. Our study is of great significance for understanding energy transfer, magnetic field evolution, and particle acceleration mechanisms in extreme astrophysical environments.