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Princeton University Astroplasmas Seminar
Black hole flares: ejection of accreted magnetic flux through 3D plasmoid-mediated reconnection
Magnetic reconnection can power bright and rapid flares originating from the inner magnetosphere of accreting black holes. We conduct extremely high resolution general-relativistic magnetohydrodynamics simulations, capturing plasmoid-mediated reconnection in a 3D magnetically arrested disk for the first time. We will show that an equatorial, plasmoid-unstable current sheet forms in a transient, non-axisymmetric, low-density magnetosphere within the inner ten Schwarzschild radii. Magnetic flux is expelled from the event horizon through reconnection at the converged universal plasmoid-mediated rate in this current sheet. The reconnection is fed by the highly-magnetized plasma in the jet, heating the plasma trapped in flux tubes to temperatures proportional to the jet's magnetization. Expelled flux tubes can orbit for an orbital period as low-density hot spots, in accordance 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 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.