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Photon bubbles in accretion discs |
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| Authors: | Charles F Gammie |
| Institution: | Institute of Astronomy, Madingley Road, Cambridge CB3 0HA,;Center for Astrophysics, MS-51, 60 Garden Street, Cambridge MA,;Isaac Newton Institute, 20 Clarkson Road, Cambridge CB3 0EH |
| Abstract: | We show that radiation-dominated accretion discs are likely to suffer from a 'photon bubble' instability similar to that described by Arons in the context of accretion on to neutron star polar caps. The instability requires a magnetic field for its existence. In an asymptotic regime appropriate to accretion discs, we find that the overstable modes obey the remarkably simple dispersion relation ο Here g is the vertical gravitational acceleration, B is the magnetic field, and F is a geometric factor of order unity that depends on the relative orientation of the magnetic field and the wavevector. In the non-linear outcome it seems likely that the instability will enhance vertical energy transport and thereby change the structure of the innermost parts of relativistic accretion discs. |
| Keywords: | accretion accretion discs instabilities MHD |