Disc formation in turbulent cloud cores: is magnetic flux loss necessary to stop the magnetic braking catastrophe or not?

Type Journal Article
Names R. Santos-Lima, E. M. de Gouveia Dal Pino, A. Lazarian
Publication Monthly Notices of the Royal Astronomical Society
Volume 429
Pages 3371-3378
Journal Abbreviation Monthly Notices of the Royal Astronomical Society
Date March 1, 2013
DOI 10.1093/mnras/sts597;
ISSN 0035-8711
Short Title Disc formation in turbulent cloud cores
URL http://adsabs.harvard.edu/abs/2013MNRAS.429.3371S
Library Catalog NASA ADS
Abstract Recent numerical analysis of Keplerian disc formation in turbulent, magnetized cloud cores by Santos-Lima et al. demonstrated that reconnection diffusion is an efficient process to remove the magnetic flux excess during the buildup of a rotationally supported disc. This process is induced by fast reconnection of the magnetic fields in a turbulent flow. In a similar numerical study, Seifried et al. concluded that reconnection diffusion or any other non-ideal magnetohydrodynamic effects would not be necessary and turbulence shear alone would provide a natural way to build up a rotating disc without requiring magnetic flux loss. Their conclusion was based on the fact that the mean mass-to-flux ratio (μ) evaluated over a spherical region with a radius much larger than the disc is nearly constant in their models. In this paper, we compare the two sets of simulations and show that this averaging over large scales can mask significant real increases of μ in the inner regions where the disc is built up. We demonstrate that turbulence-induced reconnection diffusion of the magnetic field happens in the initial stages of the disc formation in the turbulent envelope material that is accreting. Our analysis is suggestive that reconnection diffusion is present in both sets of simulations and provides a simple solution for the `magnetic braking catastrophe' which is discussed in the literature in relation to the formation of protostellar accretion discs.
Tags ISM: magnetic fields, MHD, accretion, accretion discs, diffusion, turbulence
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