The quasars were deemed to be strange new phenomena, and initially there was considerable speculation that new laws of physics might have to be invented to account for the amount of energy that they produced. However, subsequent research has shown that the quasars bear many resemblances to the active galaxies that have been studied at closer distances. This suggests that quasars and active galaxies may be related phenomena, and that their energy output can be explained using the theory of general relativity. In that sense, the quasars are certainly strange, but perhaps are not completely new phenomena.
As we have suggested numerous times by now, the present belief is that quasars are actually closely related to AGNs such as Seyfert galaxies, blazars, or radio galaxies in that they are all very active galaxies with bright nuclei powered by enormous rotating black holes. This table compares the basic properties of quasars, radio galaxies, Seyfert galaxies, and BL Lac objects. In the unified model that we shall discuss further in the next module, the differences among quasars and various AGNs is mostly a matter of the distance of the AGN from us, whether the region of the central engine is masked from our view by dust, and how rapidly matter is feeding the black hole.