Moving-mesh non-ideal magnetohydrodynamical simulations of the collapse of cloud cores to protostars

ABSTRACT Magnetic fields have been shown both observationally and through theoretical work to be an important factor in the formation of protostars and their accretion discs. Accurate modelling of the evolution of the magnetic field in low-ionization molecular cloud cores requires the inclusion of non-ideal magnetohydrodynamics (MHD) processes, specifically Ohmic and ambipolar diffusion and the Hall effect. These have a profound influence on the efficiency of magnetic removal of angular momentum from protostellar discs and simulations that include them can avoid the ‘magnetic-braking catastrophe’ in which discs are not able to form. However, the impact of the Hall effect, in particular, is complex and remains poorly studied. In this work, we perform a large suite of simulations of the collapse of cloud cores to protostars with several non-ideal MHD chemistry models and initial core geometries using the moving-mesh code arepo. We find that the efficiency of angular momentum removal is significantly reduced with respect to ideal MHD, in line with previous results. The Hall effect has a varied influence on the evolution of the disc which depends on the initial orientation of the magnetic field. This extends to the outflows seen in a subset of the models, where this effect can act to enhance or suppress them and open up new outflow channels. We conclude, in agreement with a subset of the previous literature, that the Hall effect is the dominant non-ideal MHD process in some collapse scenarios and thus should be included in simulations of protostellar disc formation.