Collapse of Rotating Magnetized Cores and Disk Formation

Details Collapse of Rotating Magnetized Cores and Disk Formation Collapse of Rotating Magnetized Cores and Disk Formation

Mar 2008

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2008aas...21116218m&link_type=abstract

American Astronomical Society, AAS Meeting #211, #162.18

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Scientific paper

Magnetic fields are usually considered dynamically important in star formation when the dimensionless mass-to-flux ratio is close to, or less than, unity (λ 1). We show that, in disk formation, the requirement is far less stringent. This conclusion is drawn from a set of 2D (axisymmetric) simulations of the collapse of rotating, singular isothermal cores magnetized to different degrees.
We find that a weak field corresponding to λ 100 can begin to disrupt the rotationally supported disk through magnetic braking. When λ ≥ 100, a more or less contiguous, rotationally supported disk is formed. For relatively strongly magnetized cores with λ ≤ 10, the disk formation is suppressed completely, as found previously. For rotationally supported disks to appear during the protostellar mass accretion phase of star formation in dense cores with realistic field strengths, the powerful magnetic brake must be weakened, perhaps through nonideal MHD effects. A dominant nonideal effect in this regime is ambipolar diffusion: the slipping of ions and neutrals and the associated magnetic diffusion in low ionization gas. Ambipolar diffusion can reduce the strength of magnetic braking by reducing the coupling of the gas to the magnetic field. Numerical simulations are required to examine the impact of ambipolar diffusion on the formation of protostellar disks.
We present results from further disk formation simulations which include the effects of ambipolar diffusion. We find qualitatively similar trends as the degree the cores are magnetized is varied, though the field diffusion results in a less centrally concetrated magnetic field.
This research was supported in part by grants from NSF and NASA.

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