Astrophysical jets: a phenomenological examination of acceleration and collimation

It is assumed that the acceleration and collimation mechanisms of jets are the same in all the classes of astrophysical objects which are observed to produce jets. These classes now include such objects as: active galactic nu clei, young stellar objects, massive X-ray binaries, low mass X-ray binarie s, black hole X-ray transients, symbiotic systems, planetary nebulae, and s upersoft X-ray sources. On the basis of this assumption, an attempt is made to identify the necessary ingredients for the acceleration and collimation mechanism. It is argued that: (i) jets are produced at the center of accre tion disks, and are accelerated and collimated hydromagnetically, and (ii) the production of powerful jets requires a hot corona or access to an addit ional energy source associated with the central object. Tentative explanati ons for the presence of jets in some classes of objects and absence in othe rs are given. Some critical observation that can test the ideas presented i n this paper are suggested. (C) 1999 Elsevier Science B.V. All rights reser ved.