What are radio galaxies?
They are galaxies emitting a significantly large amount of radiation at radio wave frequencies though not necessarily emitting a large amount of visible light. A strong radio galaxy may be emitting radio power of up to a hundred times that of an ordinary galaxy like the Milky Way.
What are Seyfert galaxies?
They are peculiar galaxies having very bright compact nuclei within which gas appears to be moving at high speed as if due to some violent activity. One per cent of all galaxies are Seyfert galaxies, named after Carl Seyfert who first investigated them in 1943.