Radiation of this type, whose intensity depends on temperature as it does for the sun and other normal stars, is called thermal radiation. A small percentage of galaxies called active galaxies emit tremendous amounts of energy. This energy results from violent events occurring in objects at their center. The distribution of the wavelengths of the emissions does not resemble that of normal stars, and so the emissions are known as nonthermal radiation. Some quasars emit 1,000 times as much energy as the entire Milky Way, yet look like stars in photographs.
Quasar is short for quasi-stellar radio source.
The name comes from the fact that the first quasars identified emit mostly radio energy and look much like stars. A radio galaxy is related to, but appears larger than, a quasar. A Seyfert galaxy is a spiral galaxy that emits large amounts of infrared rays as well as large amounts of radio waves, X rays, or both radio waves and X rays. Seyfert galaxies get their name from American astronomer Carl K. Seyfert, who in 1943 became the first person to discover one. Some active galaxies emit jets and blobs of highly energetic, electrically charged particles.