Collimation of electromagnetic beams in extragalactic radio sources

The energy transfer in extragalactic radio sources is studied in terms of strong electromagnetic beams generated inside parent galactic nuclei by a many-pulsar core or a compact rotating, magnetized object. Self-trapping by nonlinear refractive index effects is shown to be very efficient in collimating jets very close to the central core; as a consequence, a general scheme for interpreting morphological structures through the dependence of trapping on beam strength is suggested. Formation of radio lobes can be attributed to parametric instabilities of the electromagnetic wave causing the sudden termination of beams in regions of increasing density. This general outline can be applied to distorted sources also, taking into consideration propagation in inhomogeneous media.