EPoS Contribution
EPoS Contribution
Simulations of dense core collapse and disk formation with non-ideal MHD

Neil Vaytet
NBI, Copenhagen, DK
Angular momentum transport and the formation of rotationally supported structures are major issues in our understanding of protostellar core formation. Whereas purely hydrodynamical simulations lead to large Keplerian disks, ideal MHD models yield the opposite result, with essentially no disk formation. This stems from the flux-freezing condition in ideal MHD, which leads to strong magnetic braking. In this paper, we provide a more accurate description of the evolution of the magnetic flux redistribution by including resistive terms in the MHD equations. We use the adaptive mesh refinement code RAMSES to carry out the calculations. The magnetic dissipation leads to the formation of a magnetic diffusion barrier in the vicinity of the first Larson core, preventing accumulation of magnetic flux as well as amplification of the field above 0.1 G, and reorganising the field topology. This has crucial consequences on magnetic braking processes, allowing the formation of disk structures. Contrary to ideal MHD calculations, misalignment between the initial rotation axis and the magnetic field direction does not significantly affect the results, showing that the physical dissipation processes truly dominate over numerical diffusion. We also demonstrate severe limits of the ideal MHD formalism, which yield unphysical behaviours in the long-term evolution of the system. This include("he1.php"); interchange instabilities, and flux redistribution triggered by numerical diffusion.
J. Masson, U Exeter, GB
B. Commercon, ENS Lyon, FR
G. Chabrier, ENS Lyon, FR
P. Hennebelle, CEA Saclay, FR
M. Gonzalez, CEA Saclay, FR
Key publication

Suggested Session: Cores and Collapse