Is plasmoid-mediated reconnection really important in accretion flows to drive flares in AGNs?

TL;DR

This study uses high-resolution MHD simulations to demonstrate that turbulence-driven reconnection, rather than plasmoid-mediated reconnection, is the primary mechanism behind fast reconnection and flares in AGN accretion flows.

Contribution

It provides evidence that turbulence-mediated reconnection dominates over plasmoid-mediated reconnection in driving flares in AGNs, supported by 3D GRMHD simulations.

Findings

Turbulence-driven reconnection rates are about ten times higher than plasmoid-mediated rates.

Turbulence is driven by instabilities like MRI, PRTI, and CDKI in accretion flows.

3D GRMHD simulations confirm the importance of turbulence-mediated reconnection in AGNs.

Abstract

Based on very high-resolution resistive 2D and 3D magnetohydrodynamical (MHD) simulations of current sheets, our findings suggest that the answer to this question is likely no. In contrast, turbulence-mediated reconnection yields significantly faster reconnection rates - about an order of magnitude higher than the so-called universal rate for plasmoid-mediated reconnection in MHD flows ($V_\text{rec}/V_A \sim 0.01$). We conclude that turbulence-driven reconnection is the dominant mechanism responsible for fast reconnection and flares in systems such as accretion flows and relativistic jets in Active Galactic Nuclei (AGNs). In these environments, turbulence is driven by instabilities such as the magneto-rotational instability (MRI), Parker-Rayleigh-Taylor instability (PRTI), and current-driven kink instability (CDKI). Finally, we present 3D General Relativistic MHD simulations of accretion flows that confirm the crucial role of turbulence-mediated reconnection in AGN systems. These findings have important implications for understanding the origin of flares, particle acceleration, and the production of polarized radiation in these extreme environments.