Non-ideal magnetohydrodynamics on a moving mesh

TL;DR

This paper introduces new numerical schemes for non-ideal magnetohydrodynamics with resistivity in the moving-mesh code AREPO, enabling more realistic simulations of astrophysical systems where ideal MHD assumptions fail.

Contribution

The authors develop and validate explicit and implicit resistivity schemes for non-ideal MHD in AREPO, expanding the code's capabilities beyond ideal MHD approximations.

Findings

Implementation recovers analytic solutions with second-order accuracy.

Resistivity influences magnetic reconnection and gas dynamics in astrophysical simulations.

New methods enable studying complex MHD phenomena beyond ideal assumptions.

Abstract

In certain astrophysical systems the commonly employed ideal magnetohydrodynamics (MHD) approximation breaks down. Here, we introduce novel explicit and implicit numerical schemes of ohmic resistivity terms in the moving-mesh code AREPO. We include these non-ideal terms for two MHD techniques: the Powell 8-wave formalism and a constrained transport scheme, which evolves the cell-centred magnetic vector potential. We test our implementation against problems of increasing complexity, such as one- and two-dimensional diffusion problems, and the evolution of progressive and stationary Alfv\'en waves. On these test problems, our implementation recovers the analytic solutions to second-order accuracy. As first applications, we investigate the tearing instability in magnetized plasmas and the gravitational collapse of a rotating magnetized gas cloud. In both systems, resistivity plays a key role. In the former case, it allows for the development of the tearing instability through reconnection of the magnetic field lines. In the latter, the adopted (constant) value of ohmic resistivity has an impact on both the gas distribution around the emerging protostar and the mass loading of magnetically driven outflows. Our new non-ideal MHD implementation opens up the possibility to study magneto-hydrodynamical systems on a moving mesh beyond the ideal MHD approximation.