Astronomy and Astrophysics – Astronomy
Scientific paper
Aug 2001
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2001apj...557..451b&link_type=abstract
The Astrophysical Journal, Volume 557, Issue 1, pp. 451-463.
Astronomy and Astrophysics
Astronomy
12
Instabilities, Ism: Clouds, Ism: Magnetic Fields, Magnetohydrodynamics: Mhd, Turbulence
Scientific paper
Self-gravitating magnetized flows are explored numerically in slab geometry. In this approximation, the derivatives are computed only in one dimension but all three components of vector fields are retained. This is done for a range of fiducial values for the interstellar medium at the scale of molecular clouds. The overall characteristic scale of the turbulence, its Mach number, and the initial ratio of longitudinal to transverse turbulent velocities, as well as the extent of the initial density bulges within the fluid, are the main parameters of the study. Simulations have been performed with and without ambipolar drift. No external forcing is included. Velocity, density, and magnetic perturbations develop self-consistently to comparable levels in all cases. This includes those cases where the medium is initially static. However, a fully random flow produces substantially more density contrast with nested substructures. Collapse eventually occurs after typically three free-fall times. The magnetic field slows down the collapse as expected. For higher Mach numbers, the collapse is faster, and yet the peak densities reached in the final collapsed objects are lower. We have also modeled the effects of ambipolar drift in the presence of cosmic ray ionization and far-ultraviolet ionization. Because the turbulent timescales are shorter than the ambipolar drift timescales, we find that ambipolar drift does not play a significant role in gravitational collapse in a turbulent medium of the type modeled in our simulations.
Balsara Dinshaw S.
Crutcher Richard M.
Pouquet Annick
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