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Hot spots, or plasmoids, forming due to magnetic reconnection in currentsheets, are conjectured to power frequent X-ray and near-infrared flares fromSgr A*, the black hole in the center of our Galaxy. It is unclear how, where,and when current sheets form in black-hole accretion disks. We performaxisymmetric general-relativistic resistive magnetohydrodynamics simulations tomodel reconnection and plasmoid formation in a range of accretion flows.Current sheets and plasmoids are ubiquitous features which form regardless ofthe initial magnetic field in the disk, the magnetization in thequasi-steady-state phase of accretion, and the spin of the black hole. Within10 Schwarzschild radii from the event horizon, we observe plasmoids forming,after which they can merge, grow to macroscopic scales of the order of a fewSchwarzschild radii, and are ultimately advected along the jet's sheath or intothe disk. Large plasmoids are energized to relativistic temperatures viareconnection and contribute to the jet's limb-brightening. We find that onlyhot spots forming in magnetically arrested disks can potentially explain theenergetics of Sgr A* flares. The flare period is determined by the reconnectionrate, which we find to be between 0.01c and 0.03c in all cases, consistent withstudies of reconnection in isolated Harris-type current sheets. We quantifymagnetic dissipation and non-ideal electric fields which can efficiently injectnon-thermal particles. We show that explicit resistivity allows for convergednumerical solutions, such that the electromagnetic energy evolution anddissipation become independent of the grid scale for the extreme resolutionsconsidered here.

Magnetic Reconnection and Hot Spot Formation in Black Hole Accretion Disks