Mechanisms for Jets

Abstract

The evidence is now compelling that “jets” delineate the channels along which power is supplied from galactic nuclei into extended radio sources — this accumulating evidence, reported by many speakers, has been one of the major themes of this conference. Jets (often apparently one-sided) have been discovered inside many symmetrical double sources. And M87, familiar optically as a “one-sided jet” for over 60 years, is now found to have weak double radio lobes. The VLA has resolved ~ 70 jets in extended sources; there are now many instances where small jet-like structures are found on the VLBI scale; indirect arguments (some of which I’ll mention) indicate that there is directed outflow on still smaller scales, and that the primary collimation may occur right down in the central “powerhouse” (scales < 10¹⁵cm). The length-scales relevant to jet production and propagation thus span 9 orders of magnitude; the physical processes and conditions may vary widely over this vast range of scales. This paper will deal briefly with two aspects of jet physics: firstly, some direct inferences from radio maps; and, secondly, some possible mechanisms in galactic nuclei that could set up a collimated outflow.