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Magnetic flux stabilizing thin accretion disks

Magnetic flux stabilizing thin accretion disks Abstract We calculate the minimal amount of large-scale poloidal magnetic field that has to thread the inner, radiation-over-gas pressure dominated region of a thin disk for its thermal stability. Such a net field amplifies the magnetization of the saturated turbulent state and makes it locally stable. For a 10 M⊙ black hole the minimal magnetic flux is $$10^{24}(\dot{M}/\dot{M}_{\rm Edd})^{20/21}\,\rm G\cdot cm^{2}$$ . This amount is compared with the amount of uniform magnetic flux that can be provided by the companion star – estimated to be in the range $$10^{22}-10^{24}\,\rm G\cdot cm^2$$ . If accretion rate is large enough, the companion is not able to provide the required amount and such a system, if still sub-Eddington, must be thermally unstable. The peculiar variability of GRS 1915+105, an X-ray binary with the exceptionally high BH mass and near-Eddington luminosity, may result from the shortage of large scale poloidal field of uniform polarity. accretion, accretion discs, black hole physics © 2016 The Author Published by Oxford University Press on behalf of the Royal Astronomical Society http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png Monthly Notices of the Royal Astronomical Society: Letters Oxford University Press

Magnetic flux stabilizing thin accretion disks

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Publisher
Oxford University Press
Copyright
© 2016 The Author Published by Oxford University Press on behalf of the Royal Astronomical Society
ISSN
1745-3925
eISSN
1745-3933
DOI
10.1093/mnrasl/slw133
Publisher site
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Abstract

Abstract We calculate the minimal amount of large-scale poloidal magnetic field that has to thread the inner, radiation-over-gas pressure dominated region of a thin disk for its thermal stability. Such a net field amplifies the magnetization of the saturated turbulent state and makes it locally stable. For a 10 M⊙ black hole the minimal magnetic flux is $$10^{24}(\dot{M}/\dot{M}_{\rm Edd})^{20/21}\,\rm G\cdot cm^{2}$$ . This amount is compared with the amount of uniform magnetic flux that can be provided by the companion star – estimated to be in the range $$10^{22}-10^{24}\,\rm G\cdot cm^2$$ . If accretion rate is large enough, the companion is not able to provide the required amount and such a system, if still sub-Eddington, must be thermally unstable. The peculiar variability of GRS 1915+105, an X-ray binary with the exceptionally high BH mass and near-Eddington luminosity, may result from the shortage of large scale poloidal field of uniform polarity. accretion, accretion discs, black hole physics © 2016 The Author Published by Oxford University Press on behalf of the Royal Astronomical Society

Journal

Monthly Notices of the Royal Astronomical Society: Letters – Oxford University Press

Published: Jul 5, 2016

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