Jets, Magnetic Fields and the Central Engine

Abstract

Recent observations of jets unconfined by external pressure suggest that self-confinement may be common. This requires current-carrying jets with helical magnetic fields. Such beams occur in the laboratory, in lightning, and in the Crab Nebula, where currents are apparently carried over distances ≥ light year, Self-confined jets require a significant torodial magnetic field (∿10³ –10⁴ G) emerging from the nozzle. I suggest the ratio B_‖/B₀ may be the crucial nozzle parameter, causing asymmetries. Helical field configurations have remarkable stability properties and can evolve naturally as synchrotron losses in the jet lead to minimizing J→x B→. Current-carrying jets may provide a valuable clue to the physics of the central source.

Every review paper is form of disguised autobiography, and this shall be no exception. I shall treat aspects of the jet problem as it appears interesting at present, and naturally this depends on what one thinks the important problems are. Our aim is to study processes far down in the parent galaxy, and this bias selects some features of the underlying jet physics.