Short for quasi-stellar radio source. A compact, starlike celestial body with a power output greater than our entire galaxy. Believed to be the oldest and most distant objects ever detected, quasars are billions of light-years from Earth and moving away from us at nearly 80 percent of the speed of light. For this reason, quasars are highly important to astronomers' understanding of the early universe. Little is currently understood about the nature of quasars; one theory suggests that they are produced by giant black holes destroying enormous amounts of matter, causing the subsequent ejection of radiation along their north and south poles. Many astronomers believe that quasars represent an early stage in the evolution of galaxies such as our own. See also blazar, Seyfert galaxy.