2006MNRAS.368.1561M

The formation and large-scale propagation of Poynting-dominated jets produced by accreting, rapidly rotating black hole systems are studied by numerically integrating the general relativistic magnetohydrodynamic equations of motion to follow the self-consistent interaction between accretion discs and black holes. This study extends previous similar work by studying jets till t~ 10⁴GM/c³ out to r~ 10⁴GM/c², by which the jet is superfast magnetosonic and moves at a lab-frame bulk Lorentz factor of Γ∼ 10 with a maximum terminal Lorentz factor of Γ_∞≲ 10³. The radial structure of the Poynting-dominated jet is piece-wise self-similar, and fits to flow quantities along the field line are provided. Beyond the Alfvén surface at r∼ 10-100GM/c², the jet becomes marginally unstable to (at least) current-driven instabilities. Such instabilities drive shocks in the jet that limit the efficiency of magnetic acceleration and collimation. These instabilities also induce jet substructure with 3 ≲Γ≲ 15. The jet is shown to only marginally satisfy the necessary and sufficient conditions for kink instability, so this may explain how astrophysical jets can extend to large distances without completely disrupting. At large distance, the jet angular structure is Gaussian-like (or uniform within the core with sharp exponential wings) with a half-opening angle of ~5° and there is an extended component out to ~ 27°. Unlike in some hydrodynamic simulations, the environment is found to play a negligible role in jet structure, acceleration, and collimation as long as the ambient pressure of the surrounding medium is small compared to the magnetic pressure in the jet.