  Hot spots, or plasmoids, forming due to magnetic reconnection in current
sheets, are conjectured to power frequent X-ray and near-infrared flares from
Sgr 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 perform
axisymmetric general-relativistic resistive magnetohydrodynamics simulations to
model reconnection and plasmoid formation in a range of accretion flows.
Current sheets and plasmoids are ubiquitous features which form regardless of
the initial magnetic field in the disk, the magnetization in the
quasi-steady-state phase of accretion, and the spin of the black hole. Within
10 Schwarzschild radii from the event horizon, we observe plasmoids forming,
after which they can merge, grow to macroscopic scales of the order of a few
Schwarzschild radii, and are ultimately advected along the jet's sheath or into
the disk. Large plasmoids are energized to relativistic temperatures via
reconnection and contribute to the jet's limb-brightening. We find that only
hot spots forming in magnetically arrested disks can potentially explain the
energetics of Sgr A* flares. The flare period is determined by the reconnection
rate, which we find to be between 0.01c and 0.03c in all cases, consistent with
studies of reconnection in isolated Harris-type current sheets. We quantify
magnetic dissipation and non-ideal electric fields which can efficiently inject
non-thermal particles. We show that explicit resistivity allows for converged
numerical solutions, such that the electromagnetic energy evolution and
dissipation become independent of the grid scale for the extreme resolutions
considered here.
