Jet launching from the Kerr black hole magnetosphere: An electrogeodesic approach

TL;DR

This paper presents an analytical model for jet launching from Kerr black holes based on electrogeodesic motion, providing insights into particle acceleration, stability, and observational signatures in astrophysical jets.

Contribution

It introduces the first fully analytical electrogeodesic model of jet launching from Kerr magnetospheres, elucidating particle trajectories and stability conditions.

Findings

Particles are accelerated only within a specific region depending on black hole spin and magnetization.

Derived a criterion for stable latitudinal equilibrium at the rotation axis.

Provided expressions for magnetic frame-dragging and blueshifted particle emission.

Abstract

The launch of relativistic jets of plasma on astrophysical to cosmological scales is observed in a variety of astrophysical sources, from active galactic nuclei to X-ray binaries. While these jets can be reproduced by general relativistic magneto-hydrodynamics (GRMHD) and particle-in-cells (GRPIC) simulations of the dynamical Kerr magnetosphere, the development of analytic models to describe the physics of the jets has remained limited. A key challenge is to analytically describe the individual trajectories of accelerated charged particles, which ultimately build up the jet and emit radiation. In this work, we provide a first simple but fully analytical model of jet launching from the Kerr magnetosphere based on the motion of charged particles. To that end, we use the integrability of electrogeodesic motion in the Kerr monopole magnetosphere to study the ejection of charged particles near the poles. This enables us to derive (i) a criterion for the rotation axis to constitute a stable latitudinal equilibrium position, thereby representing an idealized jet, (ii) the expression for the magnetic frame-dragging effect, and (iii) the condition for an asymptotic observer to measure blueshifted particles emanating from the black hole surroundings. Our study reveals that particles can be accelerated only in a specific region whose maximal radius depends on the spin and magnetization of the black hole. Alongside these results, we provide a detailed review of the construction of test magnetospheres from (explicit and hidden) symmetries of the Kerr geometry and the condition for the separability of the electrogeodesic motion in a test magnetosphere, which serves as a basis for the model studied in this work.