A galaxy emitting a large amount of energy from a central compact source. Such a galaxy shows activity similar to that of a quasar. It is not known whether all galaxies undergo this type of behavior at some time, or if active galaxies are different from the majority of galaxies. There are a few main types of active galaxies. Seyfert galaxies, named for US astronomer Carl Seyfert, who identified the first ones in 1943, have optically bright centers, but are much less energetic than quasars and much more numerous. Most Seyfert galaxies are spirals or barred spirals. Radio galaxies are unusually strong sources of radio emission. At radio lengths, they show structure similar to that of quasars, with symmetric lobes and often a jet, but their centers are not as bright optically. A blazar is another kind of active galaxy. Blazars are more luminous and more variable than standard quasars.