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Abstract Magnetic reconnection can power bright, rapid flares originating from the inner magnetosphere of accreting black holes. We conduct extremely high-resolution (5376 × 2304 × 2304 cells) general-relativistic magnetohydrodynamics simulations, capturing plasmoid-mediated reconnection in a 3D magnetically arrested disk for the first time. We show that an equatorial, plasmoid-unstable current sheet forms in a transient, nonaxisymmetric, low-density magnetosphere within the inner few Schwarzschild radii. Magnetic flux bundles escape from the event horizon through reconnection at the universal plasmoid-mediated rate in this current sheet. The reconnection feeds on the highly magnetized plasma in the jets and heats the plasma that ends up trapped in flux bundles to temperatures proportional to the jet’s magnetization. The escaped flux bundles can complete a full orbit as low-density hot spots, consistent with Sgr A* observations by the GRAVITY interferometer. Reconnection near the horizon produces sufficiently energetic plasma to explain flares from accreting black holes, such as the TeV emission observed from M87. The drop in the mass accretion rate during the flare and the resulting low-density magnetosphere make it easier for very-high-energy photons produced by reconnection-accelerated particles to escape. The extreme-resolution results in a converged plasmoid-mediated reconnection rate that directly determines the timescales and properties of the flare.
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This content will become publicly available on October 15, 2026
Driven Collisionless Reconnection of Force-free Flux Tubes: From Onset to Coalescence
Abstract We investigate the onset of driven collisionless reconnection and plasmoid formation in a magnetically dominated pair plasma, using 2D particle-in-cell simulations. Two force-free flux tubes of radiusRare initially pushed together with a prescribed velocity, forming a current sheet whose width shrinks until reconnection sets in. Even in our largest simulation withR ≈ 1600 plasma skin depths, the sheet thickness at reconnection onset is comparable to the skin depth. Plasmoid chains develop when the sheet length-to-width aspect ratioA ≳ 30. In the strongly magnetized limit, the onset of reconnection occurs in roughly 2–6 light-crossing times, depending on the imposed driving timescale, which controls the duration of the thinning phase. In the subsequent nonlinear merging phase, the evolution becomes effectively independent of the initially imposed velocity, leading to magnetic-energy dissipation consistent with a normalized reconnection rate ∼0.1. Our results have important implications for explosive release of magnetic energy in magnetospheres of astrophysical compact objects and their surroundings.
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- Award ID(s):
- 2308944
- PAR ID:
- 10692468
- Publisher / Repository:
- American Astronomical Society
- Date Published:
- Journal Name:
- The Astrophysical Journal
- Volume:
- 992
- Issue:
- 2
- ISSN:
- 0004-637X
- Page Range / eLocation ID:
- 193
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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