Formation of protostars and the launching of stellar core outflows with moving-mesh radiation non-ideal magnetohydrodynamics

Abstract

We present an implementation of radiative transfer with flux-limited diffusion (FLD) for the moving-mesh code {\small AREPO} and use the method in a physical model for the formation of protostars with non-ideal radiation-magnetohydrodynamics (RMHD). We follow previous work in splitting the additional terms to the hydrodynamical equations arising from the inclusion of radiation into terms to be integrated explicitly and implicitly, as the diffusion and coupling terms would impose very restrictive timestep criteria. We validate the scheme with standard test problems for radiation diffusion, matter-gas coupling, and radiative shocks from the literature. Our implementation is compatible with local timestepping, which often presents problems for implicit schemes, and we found very good agreement with results obtained with global timesteps. We present an example application of the new implementation to the collapse of a $1\,{\rm M}_\odot$ molecular cloud core to a second Larson core modelled with radiation non-ideal magnetohydrodynamics. A high-velocity jet with v$_{\rm rad}> 10\, {\rm km\,s^{-1}}$ is self-consistently launched from the second core, nested within the first core, which produces a lower-velocity magnetorotational outflow. We observe magnetic field amplification up to more than $\vert \mathbf{B}\vert_{\rm max}>10^5$ G in the second core, which is surrounded by a small (<0.5 au) disk. This application demonstrates the robustness of our scheme in multi-scale and high-resolution simulations on arbitrary meshes and, as such, the model can be readily used for further simulations of protostar formation at high resolution.