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Molecular Cloud Cores and Protostars: Offsprings of Gravity and Cosmic Magnetism

Published online by Cambridge University Press:  19 July 2016

Telemachos Ch. Mouschovias
Telemachos Ch. Mouschovias*
Affiliation:
University of Illinois at Urbana-Champaign Departments of Physics and Astronomy 1011 West Springfield Avenue Urbana, IL 61801, U. S. A.

Abstract

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The formation of cloud cores (or fragments) and their evolution into protostars are the inevitable outcome of the struggle between gravity and magnetic fields, with ambipolar diffusion as the agent employed to weaken gravity's fierce opponent. The very specific and crucial role of magnetic fields in star formation deduced from detailed quantitative calculations is summarized. Criteria for collapse against magnetic and thermal-pressure forces are given. Magnetic braking time scales for both aligned and perpendicular rotators, and ambipolar diffusion time scales in both quasistatically and dynamically contracting cores are presented, and their implications are discussed. The possible role of magnetic fields in the determination of the initial (stellar) mass function (IMF) is beginning to emerge. New calculations on the axisymmetric collapse of clouds due to ambipolar diffusion reveal that the relation Bc ∞ ρ c 1/2 between the magnetic field strength and the gas density in typical cloud cores holds even in the presence of ambipolar diffusion up to densities ~ 109 cm−3. Small masses, high densities, and strong fields observed in H2O masers are consistent with theoretical calculations.

Information

Type
6. Magnetic Fields in Molecular Clouds, Dark Globules and in the Pre-Stellar and Circumstellar Environment
Information
Symposium - International Astronomical Union , Volume 140: Galactic and Intergalactic Magnetic Fields , 1990 , pp. 269 - 279
Copyright
Copyright © Kluwer 1990 

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