Cosmic Radio Jets

Extragalactic radio sources, including quasars, are now typically understood as being produced by a pair of nearly symmetric, oppositely directed relativistic jets. While some these sources span megaparsecs, and are thus the largest physically connected structures in the universe, emitting regions identified as jets have now been found on all scales down to fractions of a parsec, and jets appear to be a common element of most (maybe all) types of active galactic nuclei (AGN). We first summarize key observations of different classes of cosmic radio jets, and describe how they may be connected. Theoretical models for the launching and propagation of extragalactic jets are briefly described. All of these models assume a magnetized plasma, which typically amounts to only a small fraction of the accreted gas, is ejected from the vicinity of a supermassive black hole. The extreme complexity of the relevant physics has demanded numerical simulations to examine non-linear effects on the stability of propagating jets, and some recent results from these efforts are summarized.