Seyfert
galaxies, first recognized by Carl Seyfert in 1943, are galaxies that have extremely bright, almost starlike, nuclei.
The spectra of the nuclei show strong emission lines, indicative of a strong
source of high-speed electrons that can produce ultraviolet radiation by the synchrotron process. The emitting region is usually about 1,000 parsecs (see parsec) wide, and the final source is now commonly taken to be a large black hole at the centers of these tidally active
galaxies. The radio luminosities of Seyferts are intermediate between those of normal galaxies and those of radio galaxies, and Seyferts are considered to lie between normal galaxies and quasars in the degree of activity in their nuclei. About 2 percent of all galaxies are Seyferts (see extragalactic systems).