EVOLUTION OF POWERFUL EXTRAGALACTIC RADIO-SOURCES

Observations of complete flux density limited samples of powerful extr agalactic radio sources by very-long-baseline interferometry enable us to study the evolution of these objects over the range of linear scal es from I parsec to 15 kiloparsecs (1 parsec = 3.09 x 10(18) cm). The observations are consistent with the unifying hypothesis that compact symmetric objects evolve into compact steep-spectrum doubles, which in turn evolve into large-scale Fanaroff-Riley class II objects. It is s uggested that this is the primary evolutionary track of powerful extra galactic radio sources. In this case there must be significant luminos ity evolution in these objects, but little velocity evolution, as they expand from 1 parsec to several hundred kiloparsecs in overall size.