Can non-ideal magnetohydrodynamics solve the magnetic braking catastrophe?
Bate, Matthew R.
Monthly Notices of the Royal Astronomical Society
Oxford University Press (OUP)
© 2016 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society.
We investigate whether or not the low ionization fractions in molecular cloud cores can solve the 'magnetic braking catastrophe', where magnetic fields prevent the formation of circumstellar discs around young stars.We perform three-dimensional smoothed particle nonideal magnetohydrodynamics (MHD) simulations of the gravitational collapse of one solar mass molecular cloud cores, incorporating the effects of ambipolar diffusion, Ohmic resistivity and the Hall effect alongside a self-consistent calculation of the ionization chemistry assuming 0.1 μm grains. When including only ambipolar diffusion or Ohmic resistivity, discs do not form in the presence of strong magnetic fields, similar to the cases using ideal MHD.With the Hall effect included, disc formation depends on the direction of the magnetic field with respect to the rotation vector of the gas cloud. When the vectors are aligned, strong magnetic braking occurs and no disc is formed. When the vectors are anti-aligned, a disc with radius of 13 au can form even in strong magnetic when all three non-ideal terms are present, and a disc of 38 au can form when only the Hall effect is present; in both cases, a counter-rotating envelope forms around the first hydrostatic core. For weaker, anti-aligned fields, the Hall effect produces massive discs comparable to those produced in the absence of magnetic fields, suggesting that planet formation via gravitational instability may depend on the sign of the magnetic field in the precursor molecular cloud core.
t. This work was funded by an Australian Research Council (ARC) Discovery Projects Grant (DP130102078), including a Discovery International Award funding MRB’s sabbatical at Monash. DJP is funded by ARC Future Fellowship FT130100034. MRB also acknowledges support from the European Research Council under the European Community’s Seventh Framework Programme (FP7/2007- 2013 grant agreement no. 339248). We would like to thank Mark Wardle for helpful discussions and clarifications. This work was supported by resources on the gSTAR national facility at Swinburne University of Technology. gSTAR is funded by Swinburne and the Australian Government’s Education Investment Fund.
This is the final version of the article. Available from the publisher via the DOI in this record.
Vol. 457, pp. 1037 - 1061