Notes on the Discovery of Active Galaxies and Quasars 1943 American Astronomer Karl Seyfert undertakes a study of spiral galaxies with star-like nuclei and strong emission lines in their spectra. We now call them Seyfert galaxies. 1950 Australian radio astronomer John Bolton discovers the cosmic radio sources Cygnus A , Virgo A , and Centaurus A, and identifies them as galaxies. 1960 English radio astronomers complete the 3rd Cambridge Catalog, listing the brightness and positions of a few hundred cosmic radio sources. Many of these radio sources are coincident with distant galaxies.
Astronomers discover hundreds of quasars, radio galaxies, and active galaxies.
They find that many of these sources vary in brightness on timescales of days to years. 1978 NASA launches the Einstein Observatory , the first imaging X-ray telescope. They find that virtually all Seyfert galaxies and quasars are luminous X-ray sources. Radio astronomers, working with the new VLA telescope and the Merlin telescope in England, map the radio emission from hundreds of radio galaxies and quasars. They find that the radio sources typically have jets emanating from a compact nucleus and terminating in lobes of radio emission far beyond the optical galaxy.