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Viscosity and Large-Scale Magnetic Fields from Accretion Disc Dynamos

Published online by Cambridge University Press:  12 April 2016

Christopher A. Tout
Christopher A. Tout*
Affiliation:
Konkoly Observatory of the Hungarian Academy of Sciences, H–1525 Budapest, P.O.B. 67, Hungary.

Abstract

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We review those processes associated with accretion discs that are probably influenced by magnetic fields, specifically, accretiondisc viscosity, energy dissipation and jet formation. We consider how magnetic instabilities in the disc can lead to a self-sustaining dynamical dynamo and how this is manifested as magnetohydrodynamic turbulence in numerical simulations. We show that currently these models do not fit with observational constraints imposed by dwarf-nova outbursts. We also show that the drop in ionisation fraction does not lead to the apparently necessary drop in viscosity in quiescent cataclysmic variable discs. Large-scale magnetic fields are required to launch and collimate jets form discs. We describe an inverse cascade process that can construct sufficient large-scale field from small-scale field generated by a dynamo.

Type
Part 5. Magnetic Fields and Viscosity
Information
International Astronomical Union Colloquium , Volume 163: Accretion Phenomena and Related Outflows , 1997 , pp. 190 - 200
Copyright
Copyright © Astronomical Society of the Pacific 1997

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