Ambipolar diffusion in star-forming clouds

Details Ambipolar diffusion in star-forming clouds Ambipolar diffusion in star-forming clouds

Jun 1998

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1998a%26a...334..742h&link_type=abstract

Astronomy and Astrophysics, v.334, p.742-745 (1998)

Astronomy and Astrophysics

Astrophysics

6

Stars: Formation, Ism: Clouds, Ism: Magnetic Fields, Mhd

Scientific paper

The dynamical collapse of a magnetically supported molecular cloud with ambipolar diffusion (hereafter AD) is numerically investigated. Each of the five cloud models considered here has a fixed mass of 1{cal M}sun, a prescribed outer boundary where the normal derivative of the total pressure vanishes. In these models, there is no dynamical collapse if AD is excluded. It is shown that owing to the strong non-linearity exhibiting the effective AD term, AD appears to be operating in different regions with completely different time scales. The models with AD undergo dynamical contraction on a dilute free-fall time scale (tau_ {ff}) ranging between 1.1-3.0 tau_ {ff}, depending on the ionization fraction in the cloud considered. It is shown that a shock is always formed at the center which thereafter propagates radially outwards into the high latitudinal regions leaving quasi magnetohydrostatic density profiles behind its shock front. If AD is present, these structures do not survive and start to collapse to form a central point mass surrounded by a highly condensed disk-like configuration. Thus, AD is actually able to change the flow configuration on time scales comparable to fractions of tau_ {ff}. Furthermore, AD appears to give rise to an inside-outside collapse via a magnetosonic expansion wave which starts its motion from the center.

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