The role of magnetic fields in star formation
arXiv:0903.1673
Abstract
Star formation is thought to be triggered by the gravitational collapse of the dense cores of molecular clouds. Angular momentum conservation during the collapse results in the progressive increase of the centrifugal force, which eventually halts the inflow of material and leads to the development of a central mass surrounded by a disc. In the presence of an angular momentum transport mechanism, mass accretion onto the central object proceeds through this disc, and it is believed that this is how stars typically gain most of their mass. However, the mechanisms responsible for this transport of angular momentum are not well understood. The most promising are turbulence viscosity driven by the magnetorotational instability (MRI), and outflows accelerated centrifugally from the surfaces of the disc. Both processes are powered by the action of magnetic fields and are, in turn, likely to strongly affect the structure, dynamics, evolutionary path and planet-forming capabilities of their host discs. The weak ionization of protostellar discs, however, may prevent the magnetic field from effectively coupling to the gas and drive these processes. Here I examine the viability and properties of these magnetically driven processes in protostellar discs. The results indicate that, despite the weak ionization, the field is able to couple to the gas and shear for fluid conditions thought to be satisfied over a wide range of radii in these discs.
arXiv comment8 pages, 6 figures. In Australian Space Science Conference Series: 8th Conference Proceedings NSSA Full Referreed Proceedings CD, (ed) National Space Society of Australia Ltd, edt. W. Short, I. Cairns. Conference held in Canberra, Australia September 29- October 01, 2008, ISBN 13:978-0-9775740-2-5
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