Wednesday 08 Nov 2017Misaligned black hole accretion discs

Dr. Rebecca Nealon - University of Leicester

Physics, 4th Floor 14:00-15:00

Accretion discs around rotating black holes are often assumed to be aligned with the black hole spin. Relaxing this assumption by inclining the disc means that the rotation of the black hole is able to affect the disc evolution, leading to previously unexplored structures in the disc. I will present three-dimensional simulations investigating the evolution of such tilted discs at a range of inclinations. In the small inclination case we identify an oscillatory disc profile, in agreement with previous analytical predictions. In the high inclination case we confirm disc breaking and tearing, where the disc is torn in independently precessing rings of gas. I will then consider applications of these structures to observational features, considering the currently unexplained phenomenon of quasi-periodic oscillations. Turning to geometrically thick accretion flows we consider a torus (with a donut shaped profile), such as would form from a tidal disruption event. However simulating a torus in three-dimensions is difficult as they may be unstable to the non-axisymmetric hydrodynamic Papaloizou-Pringle instability. I will present our simulations of an idealised, circularised torus that has similar parameters to a previously simulated tidal disruption remnant and show that i) it is unstable to this instability and ii) this instability is capable of driving angular momentum transfer. Our simulations imply that the initial accretion rate (and hence lightcurve) of tidal disruption events may be constrained by this instability rather than the magneto-rotational instability.

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