From: Zardoz ® 04/11/2001 19:37:47 Subject: re: COSMOLOGY FAQ post id: 484073 What are quasars ? From: Geraint ® Quasars are part of the family known as "active galaxies" and are the most luminous objects in the universe (other than the sporadic gamma ray bursts). They are seen through-out the universe, some close by, but the vast majority in the distant (and therefore early) universe. They are physically located at the centres of galaxies, in regions not much bigger than the size of the solar system, but output more energy than the 1012 stars in a galaxy. Their spectra show that they contain gas swirling round at 1000s of km/s, as well as X-ray and gamma ray emission. There is a lot of ultraviolet also. All this is the signature of material swirling around a supermassive black hole, the only power source efficient enough to be in such a small volume. While you can see the rest of the galaxy in nearby quasars, more distant ones appear point-like - hence the name ( quasar = quasi-stellar object ). Some have radio emission and giant jets, some don't. Most are variable, suggesting that there are a lot of things going on in this small central region of galaxies. Quasars and active galaxies are a large part of modern astronomy, studied at all wavelengths and by a lot of theorists (my wife being one of them).