Black hole flares: ejection of accreted magnetic flux regulated by plasmoid-dominated reconnection

Magnetic reconnection is conjectured to power bright and rapid flares originating from the inner magnetospheres in accreting black holes. We conduct extreme resolution three-dimensional general relativistic magnetohydrodynamics simulations of a magnetically arrested black hole accretion disk showing that a transient, non-axisymmetric, highly magnetized magnetosphere can form in the inner 10 Schwarzschild radii accompanied by a drop in mass accretion rate. A macroscopic equatorial current sheet establishes in the magnetosphere, extending from the event horizon to the accretion disk. Magnetic flux is expelled from the horizon through magnetic reconnection in this current sheet fed by the highly magnetized surrounding plasma in the black hole jet. Reconnection heats plasmoids, or flux tubes, to temperatures proportional to the magnetization in the jet. The hot flux tubes that are expelled from the exhaust of the reconnection layer can power bright TeV flares as observed from M87. The timescales of the flare are directly determined by the reconnection rate in the plasmoid-dominated regime. The flux tubes can orbit in the disk for an orbital period, as low-density hot spots.