Open AccessPhoton bubbles in accretion discs
Author(s) -
Gammie Charles F.
Publication year - 1998
Publication title -
monthly notices of the royal astronomical society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.058
H-Index - 383
eISSN - 1365-2966
pISSN - 0035-8711
DOI - 10.1046/j.1365-8711.1998.01571.x
Subject(s) - physics , accretion (finance) , neutron star , astrophysics , instability , magnetic field , photon , polar , intermediate polar , context (archaeology) , dispersion relation , radiation , astronomy , mechanics , condensed matter physics , optics , stars , quantum mechanics , white dwarf , paleontology , biology
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 2 =−i gkF ( B , k ). 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.