http://arxiv.org/abs/2003.04330
Hot spots, or plasmoids, forming due to magnetic reconnection in thin current sheets, are conjectured to power frequent bright X-ray and near-infrared flares from Sgr A*, the supermassive black hole in the center of our Galaxy. It is of yet unclear how, where, and when such thin current sheets form in black-hole accretion disks or astrophysical jets. In this work we perform axisymmetric general-relativistic resistive magnetohydrodynamics simulations to model magnetic reconnection and associated plasmoid formation in a wide range of accretion flows. We show that current sheets and plasmoids are ubiquitous features which form regardless of the initial size of the disk and the magnetization in the quasi-steady-state phase of accretion. In all cases we observe plasmoids forming in current sheets close to the event horizon within 5 to 10 Schwarzschild radii. These plasmoids can then merge, grow to macroscopic scales of the order of a Schwarzschild radius, and are ultimately advected along the jet’s sheath or into the disk. The largest plasmoids are efficiently energized to relativistic temperatures via magnetic reconnection and contribute to the heating of the jet’s sheath. In all cases we find reconnection rates between 0.01c and 0.03c, consistent with studies of reconnection in isolated Harris-type current sheets. We quantify magnetic dissipation and strong non-ideal electric fields which can efficiently inject non-thermal particles. We also show that an explicit resistivity allows for converged numerical solutions, such that the electromagnetic energy density evolution and dissipation become independent of the grid scale for the extreme resolutions considered here.
B. Ripperda, F. Bacchini and A. Philippov
Wed, 11 Mar 20
45/65
Comments: submitted to ApJ