Pair Drizzle around Sub-Eddington Supermassive Black Holes

TL;DR

This study uses radiation GRMHD simulations to analyze electron-positron pair creation near sub-Eddington supermassive black holes, confirming pair drizzle's role in maintaining charge density and its peak along the jet-disk boundary.

Contribution

It extends previous work by applying radiation GRMHD simulations to low-magnetization accretion flows, providing new insights into pair production mechanisms near supermassive black holes.

Findings

Pair drizzle maintains high charge density in the magnetosphere.

Pair production peaks at the jet-disk boundary.

Simulation confirms pair drizzle's significance in M87.

Abstract

Electron-positron pair creation near sub-Eddington accretion rate black holes is believed to be dominated by the Breit-Wheeler process (photon-photon collisions). The interacting high energy photons are produced when unscreened electric fields accelerate leptons either in coherent, macroscopic gaps or in incoherent structures embedded in the turbulent plasma flow. The latter type of acceleration results in a drizzle of pair production sourced by photons from the background radiation field whose energies are near the pair-production threshold. In this work, we use radiation GRMHD simulations to extend an earlier study of pair drizzle by Moscibrodzka et al. We focus on low-magnetization (SANE) accretion onto supermassive Kerr black holes and consider radiation due to synchrotron, bremsstrahlung, and Compton upscattering processes. We confirm that pair drizzle in M87 is sufficient to keep the magnetospheric charge density orders of magnitude above the Goldreich-Julian density. We also find that pair production peaks along the jet-disk boundary.