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Register a new userThe magnetic Rayleigh-Taylor instability around astrophysical black holes
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Ioannis Contopoulos
Publication date
2018
fields
Physics
and research's language is
English
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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.
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The dynamics of a thin liquid film on the underside of a curved cylindrical substrate is studied. The evolution of the liquid layer is investigated as the film thickness and the radius of curvature of the substrate are varied. A dimensionless parameter (a modified Bond number) that incorporates both geometric parameters, gravity, and surface tension is identified, and allows the observations to be classified according to three different flow regimes: stable films, films with transient growth of perturbations followed by decay, and unstable films. Experiments and theory confirm that, below a critical value of the Bond number, curvature of the substrate suppresses the Rayleigh-Taylor instability.
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