Annu. Rev. Astron. Astrophys. 1988. 36: 539-598 Copyright © 1998 by Annual Reviews. All rights reserved

2.1. Phenomenology of an Extended Radio Source

The original phenomenological model was proposed by Rees (1971), Scheuer (1974). A pictorial scheme is illustrated in Figure 2. Twin opposite jets are produced and collimated in the innermost cores of AGNs (sizes 10^-3 pc) by some powerful engine that most likely derives its energy from accretion onto a gravitational well and thrusts continuously supersonic and/or super-Alfvènic magnetized plasma along the angular momentum axis. The twin jets plough their way through the ambient intergalactic gas, transferring energy and momentum far away from the parent core. Jets are structurally affected by the interaction with the external medium originating shocks, filaments, and wiggles. Local electron acceleration to relativistic energies supports synchrotron emission. The "head" where the jet pushes against the external medium is a turbulent working surface producing a bow shock and a cocoon around the entire source.

Figure 2. Schematic diagram of a strong radio source.