Galactic centers and twin-jets

A schematic model is suggested to describe the various activities in the centers of massive galaxies. Basic assumptions are that (i) a uniform model can account for all the observed phenomena, such as quasars, blazars, radio galaxies, Seyferts, and the centers of normal galaxies (with disks), (ii) activity in galactic centers is repetitive, and (iii) in-situ-acceleration of highly relativistic electrons (other than by adiabatic compression) has an insignificant efficiency, i.e. is ignorable. (Auth.)