Large-Scale Poloidal Magnetic Field Dynamo Leads to Powerful Jets in GRMHD Simulations of Black Hole Accretion with Toroidal Field

TL;DR

This study demonstrates that turbulence in a black hole accretion disk can generate large-scale poloidal magnetic flux in situ from a purely toroidal field, leading to powerful jets in GRMHD simulations.

Contribution

The paper shows that turbulence can produce large-scale poloidal magnetic flux from a toroidal field in 3D GRMHD simulations, resulting in highly powerful jets.

Findings

Jets are more powerful than previous simulations by a factor of 10,000.

Jets accelerate to gamma ~ 10 over three decades in distance.

Jets exhibit stability with minimal kink or pinch instabilities.

Abstract

Accreting black holes (BHs) launch relativistic collimated jets, across many decades in luminosity and mass, suggesting the jet launching mechanism is universal, robust and scale-free. Theoretical models and general relativistic magnetohydrodynamic (GRMHD) simulations indicate that the key jet-making ingredient is large-scale poloidal magnetic flux. However, its origin is uncertain, and it is unknown if it can be generated in situ or dragged inward from the ambient medium. Here, we use the GPU-accelerated GRMHD code H-AMR to study global 3D BH accretion at unusually high resolutions more typical of local shearing box simulations. We demonstrate that turbulence in a radially-extended accretion disc can generate large-scale poloidal magnetic flux in situ, even when starting from a purely toroidal magnetic field. The flux accumulates around the BH till it becomes dynamically-important, leads to a magnetically arrested disc (MAD), and launches relativistic jets that are more powerful than the accretion flow. The jet power exceeds that of previous GRMHD toroidal field simulations by a factor of 10,000. The jets do not show significant kink or pinch instabilities, accelerate to $\gamma \sim 10$ over 3 decades in distance, and follow a collimation profile similar to the observed M87 jet.