Magnetic Reconnection and Hot Spot Formation in Black Hole Accretion Disks

By B. Ripperda, F. Bacchini, A. Philippov. Astrophysical Journal, 2020

193 citations recorded by the source corpus.

Hot spots, or plasmoids, which form 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 that form regardless of the initial magnetic field in the disk, the magnetization in the quasisteady-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 and in all cases, consistent with studies of reconnection in isolated Harris-type current sheets. We quantify magnetic dissipation and nonideal electric fields, which can efficiently inject nonthermal 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.

Subfields: Astronomy and Astrophysics, Geophysics

View Paper: https://www.semanticscholar.org/paper/6a5025b5315b73dc210856eb77a7a721dab31325

How researchers see this paper

The researchers whose trusted networks rank it highest, strongest advocate first. Every researcher gets a different order.

In Astronomy and Astrophysics

In Geophysics

Citations in the corpus

First Sagittarius A* Event Horizon Telescope Results. V. Testing Astrophysical Models of the Galactic Center Black Hole (2022, methodology): “For example, the first efforts have recently been made with highresolution global GRMHD simulations to capture heating through magnetic reconnection in the largest current sheets in the system (Nathanail et al. 2020; Ripperda et al. 2020; Note.”
Black Hole Flares: Ejection of Accreted Magnetic Flux through 3D Plasmoid-mediated Reconnection (2021, background): “Recently, extreme-resolution two-dimensional (2D) GRMHD simulations showed that escape of magnetic flux bundles from the black hole, resulting in the decay of magnetic flux on the horizon, occurs through plasmoid-mediated reconnection (Ripperda et al. 2020, hereafter RBP20).”