  We investigate the development of the magnetic Rayleigh-Taylor instability at
the inner edge of an astrophysical disk around a spinning central black hole.
We solve the equations of general relativity that govern small amplitude
oscillations of a discontinuous interface in a Keplerian disk threaded by an
ordered magnetic field, and we derive a stability criterion that depends on the
central black hole spin and the accumulated magnetic field. We also compare our
results with the results of GR MHD simulations of black hole accretion flows
that reach a magnetically arrested state (MAD). We found that the instability
growth timescales that correspond to the simulation parameters are comparable
to the corresponding timescales for free-fall accretion from the ISCO onto the
black hole. We thus propose that the Rayleigh-Taylor instability disrupts the
accumulation of magnetic flux onto the black hole horizon as the disk reaches a
MAD state.
