Other
Scientific paper
Dec 1992
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1992aas...181.1406c&link_type=abstract
American Astronomical Society, 181st AAS Meeting, #14.06; Bulletin of the American Astronomical Society, Vol. 24, p.1142
Other
Scientific paper
We follow numerically the self-initiated formation and contraction of cloud cores due to ambipolar diffusion (the relative motion of neutral and ionized matter) in self-gravitating, isothermal, magnetically supported molecular cloud models, accounting for a cosmic abundance of interstellar grains (both charged and neutral). Using an implicit code with an adaptive mesh, the evolution is followed to an enhancement of the central density by a factor of 10(6) (e.g., from 2.6 times 10(3) cm(-3) to 2.6 times 10(9) cm(-3) ). Ambipolar diffusion inevitably leads to the formation of thermally and magnetically supercritical cores, which contract dynamically inside magnetically supported cloud envelopes, in agreement with the early theoretical predictions of Mouschovias. The time scale for the formation of a core is essentially the ambipolar diffusion time scale tau_AD in the central flux tubes of a cloud, which is typically more than an order of magnitude greater than the free-fall time tau_ff. The grains lengthen the time scale for the formation of a core, accentuate the core-envelope separation, and increase a core's final size, mass, and magnetic flux. We present the results of two cloud models, each consistent with a dimensional temperature T=10 K, cloud mass M_cloud =~ 100 M_sun, and initial central magnetic field B_0 = 35 mu G. The first model, which neglects the macroscopic effects of grains, has at the end of our simulation a supercritical core with radius r_core = 0.092 pc, mass M_core=5.0 M_sun, reaching a central density enhancement of 10(6) (i.e., n_c = 2.6 \times 10^9 cm^{-3}) in a time t= 1.0 \times 107 yr. The second cloud model, which includes the macroscopic effects of grains, has a supercritical core at the end of our calculation with a radius r_core =0.13 pc, mass M_core = 11.6 M_sun, and reaches a central density enhancement of 10^6 at a time t = 1.9 \times 107 yr. The predicted core masses and sizes are in agreement with current observations of dense cores in molecular clouds. Theoretical predictions of other physical quantities relevant to the star formation process, such as mass infall rates, power-law density profiles, and spatial velocity structures, are also made.
Ciolek Glenn E.
Mouschovias Telemachos Ch.
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