Other
Scientific paper
Jan 2009
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2009aas...21334702m&link_type=abstract
American Astronomical Society, AAS Meeting #213, #347.02; Bulletin of the American Astronomical Society, Vol. 41, p.483
Other
Scientific paper
It is established that the formation of rotationally supported disks during the main accretion phase of star formation is suppressed by a moderately strong magnetic field in the ideal MHD limit. Non-ideal MHD effects are expected to weaken the magnetic braking, perhaps allowing the disk to reappear. I concentrate on one such effect, ambipolar diffusion, which enables the field lines to slip relative to the bulk neutral matter.
I will report the results of a set of 2D (axisymmetric) simulations of the collapse of rotating, singluar isothermal cores with different degrees of magnetization and cosmic ray ionization. I demonstrate that the slippage does not sufficiently weaken the braking to allow rotationally supported disks to form for realistic levels of cloud magnetization and cosmic rayionization rate; in some cases, the magnetic braking is even enhanced. Only in dense cores with both exceptionally weak fields and unreasonably low ionization rate do such disks start to form in our simulations. I conclude that additional processes, such as Ohmic dissipation or Hall effect, are needed to enable disk formation. Alternatively, the disk may form at late times when the massive envelope that anchors the magnetic brake is dissipated, perhaps by a protostellar wind. This research was supported in part by grants from NSF and NASA.
Li Zaidong
Mellon Richard R.
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