Particle Acceleration via Transient Stagnation Surfaces in MADs During Flux Eruptions

TL;DR

This paper uses GRMHD simulations to identify a novel transient stagnation surface during flux eruptions in MADs, which could serve as a new particle acceleration mechanism near supermassive black holes.

Contribution

First report of a persistent transient stagnation surface in MADs during flux eruptions, providing a potential new particle acceleration site near black holes.

Findings

Identified a stagnation surface at 2-3 r_g from the black hole.

Estimated potential difference of ~10^{16} Volts along the surface.

Suggests a new mechanism for charged particle acceleration in MADs.

Abstract

In this study, we focus on the simulation of accretion processes in Magnetically Arrested Disks (MADs) and investigate the dynamics of plasma during flux eruption events. We employ general relativistic magneto-hydrodynamic (GRMHD) simulations and search for regions with a divergent velocity during a flux eruption event. These regions would experience rapid and significant depletion of matter. For this reason, we monitor the activation rate of the floor and the mass supply required for stable simulation evolution to further trace this transient stagnation surface. Our findings reveal an unexpected and persistent stagnation surface that develops during these eruptions, located around 2-3 gravitational radii (${\rm r_g}$) from the black hole. The stagnation surface is defined by a divergent velocity field and is accompanied by enhanced mass addition. This represents the first report of such a feature in this context. The stagnation surface is ($7-9\,\,{\rm r_g}$) long. We estimate the overall potential difference along this stagnation surface for a supermassive black hole like M87 to be approximately $\Delta V \approx 10^{16}$ Volts. Our results indicate that, in MAD configurations, this transient stagnation surface during flux eruption events can be associated with an accelerator of charged particles in the vicinity of supermassive black holes. In light of magnetic reconnection processes during these events, this work presents a complementary or an alternative mechanism for particle acceleration.