Active galaxies are recently discovered because researcher emphasized on radio observation which enabled scientists to study objects which are not in the visible wave range such as quasars and active galaxies. Synchrotron radiation also help to study the motion of gas in the accretion disc and the radio lobes.
Active galaxies are brighter than normal galaxies but fainter than quasars.
We know several different active galaxies such as galaxies with jets and beams, peculiar galaxies, which seem to rip themselves apart, and Seyfert galaxies which contains extremely hot gas in its disc and varies in its brightness. Seyfert galaxies are also consider as low-luminosity quasars. Active galaxies lie in the center of two immense radio sources called radio lobes and it is believed that a massive black hole lies in the middle of the active galaxy functioning as an engine. The radio lobes are feeding the accretion disc around the energy source. The material in this disk gets so highly compressed and heated up, that some galaxies emit radio waves in form of beams or jets shaped by magnetic fields at almost the speed of light.