Three-dimensional Simulations of AGN Jets: Magnetic Kink Instability versus Conical Shocks

TL;DR

This study uses 3D MHD simulations to investigate how AGN jets dissipate energy through magnetic kink instabilities or shocks, depending on their formation history and ambient medium interactions.

Contribution

It introduces a self-consistent simulation approach showing how different jet formation scenarios lead to distinct energy dissipation mechanisms in AGN jets.

Findings

Jets forming in new outbursts undergo magnetic kink instability and reconnection.

Jets from recurrent activity maintain stability and dissipate energy at shocks.

Dissipation regions correlate with changes in ambient gas density profiles.

Abstract

Relativistic jets in active galactic nuclei (AGN) convert as much as half of their energy into radiation. To explore the poorly understood processes that are responsible for this conversion, we carry out fully 3D magnetohydrodynamic (MHD) simulations of relativistic magnetized jets. Unlike the standard approach of injecting the jets at large radii, our simulated jets self-consistently form at the source and propagate and accelerate outward for several orders of magnitude in distance before they interact with the ambient medium. We find that this interaction can trigger strong energy dissipation of two kinds inside the jets, depending on the properties of the ambient medium. Those jets that form in a new outburst and drill a fresh hole through the ambient medium fall victim to a 3D magnetic kink instability and dissipate their energy primarily through magnetic reconnection in the current sheets formed by the instability. On the other hand, those jets that form during repeated cycles of AGN activity and escape through a pre-existing hole in the ambient medium maintain their stability and dissipate their energy primarily at MHD recollimation shocks. In both cases the dissipation region can be associated with a change in the density profile of the ambient gas. The Bondi radius in AGN jets serves as such a location.