Black-hole accretion flares from magnetic Rayleigh-Taylor instability

The magnetic Rayleigh-Taylor instability (RTI) is a fundamental process in astrophysical plasmas, occurring at density interfaces perturbed by gravity. In collisionless accretion flows around supermassive black holes such as Sgr A*, the RTI may be triggered at the interface between highly magnetized cavities (sporadically ejected through magnetic reconnection from the jet base) and the ambient flow. In addition to mixing the plasma, the RTI may convert free gravitational energy into nonthermal particle acceleration (required to explain near-infrared flares). To determine the viability of this scenario, we perform local kinetic particle-in-cell simulations of the RTI involving a plasma slab on top of a highly magnetized cavity, with a sheared magnetic field. We show that the RTI develops small plumes that merge and grow to progressively larger scales until the formation of a large-scale plume, which triggers relativistic magnetic reconnection upon relaxation. We find that the RTI ultimately causes efficient particle acceleration capable of fueling near-infrared flares from the inner accretion flow in Sgr A*.