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arXiv · 1606.09566

Magnetic flux stabilizing thin accretion disks

Aleksander Sadowski
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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 $10 M_\odot$ 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.

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Aleksander Sadowski. 2016-06-30. Magnetic flux stabilizing thin accretion disks. https://doi.org/10.1093/mnras%2Fstw1852

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