Astrophysical jets

I show that the assumption that the acceleration and collimation mechanisms of jets are the same in all the classes of astrophysical objects which are observed to produce jets, can lead to interesting conclusions. Jets have now been observed in active galactic nuclei, young stellar objects, massive X-ray binaries, low-mass X-ray binaries, black-hole X-ray transients, symbiotic systems, planetary nebulae, and supersoft X-ray sources, and possibly recurrent novae and pulsars. An attempt is made to identify the necessary ingredients for the acceleration and collimation mechanisms. I show that most likely: (1) jets are produced at the center of accretion disks, and are accelerated and collimated hydromagnetically, and (2) the production of powerful jets may require a hot corona or access to an additional heat/wind source associated with the central object. Tentative explanations for the presence of jets in some classes of objects and absence in others are given. Some critical observations that can test the ideas presented in this paper are suggested.