The onset and breakdown of black hole flares

Abstract: The unique electromagnetic and gravitational properties of black holes and their magnetospheres, accretion disks, jets, and coronae, make them the perfect laboratory to study extreme plasma physics. Recent breakthroughs in observations of event-horizon-scale plasma flows near Sgr A* and M87* allow us to probe fundamental plasma dynamics in extreme high-energy environments. Black holes are also known as powerful sources of multiwavelength electromagnetic emission in the form of flares. The dynamics of the strongly magnetized plasma that produces these emission signatures is still poorly understood. With unprecedented accuracy in general relativistic magnetohydrodynamics simulations we find that the interplay of interchange, ballooning and tearing instabilities drives the accretion flow to form large-scale current sheets at the event horizon. We investigate in detail how these ideal and non-ideal instabilities affect the transport of magnetic flux and angular momentum, that eventually leads to a cycle of flares in magnetically arrested accretion flows.