Multifluid magnetohydrodynamic turbulent decay

TL;DR

This study investigates how non-ideal effects like ambipolar diffusion and the Hall effect influence the decay and structure of highly turbulent, multifluid magnetohydrodynamic flows relevant to molecular clouds and star formation.

Contribution

It demonstrates that ambipolar diffusion accelerates turbulence decay and steepens spectral slopes, while the Hall effect has minimal impact, and shows simplified modeling can capture key physics.

Findings

Ambipolar diffusion increases turbulence decay rate.

Spectral steepening is mainly due to ambipolar diffusion.

Simplified resistive models can replicate multifluid turbulence effects.

Abstract

It is generally believed that turbulence has a significant impact on the dynamics and evolution of molecular clouds and the star formation which occurs within them. Non-ideal magnetohydrodynamic effects are known to influence the nature of this turbulence. We present the results of a suite of 512-cubed resolution simulations of the decay of initially super-Alfvenic and supersonic fully multifluid MHD turbulence. We find that ambipolar diffusion increases the rate of decay of the turbulence while the Hall effect has virtually no impact. The decay of the kinetic energy can be fitted as a power-law in time and the exponent is found to be -1.34 for fully multifluid MHD turbulence. The power spectra of density, velocity and magnetic field are all steepened significantly by the inclusion of non-ideal terms. The dominant reason for this steepening is ambipolar diffusion with the Hall effect again playing a minimal role except at short length scales where it creates extra structure in the magnetic field. Interestingly we find that, at least at these resolutions, the majority of the physics of multifluid turbulence can be captured by simply introducing fixed (in time and space) resistive terms into the induction equation without the need for a full multifluid MHD treatment. The velocity dispersion is also examined and, in common with previously published results, it is found not to be power-law in nature.