Wednesday, January 21, 2009


A quasar is an extremely intense and active galactic nucleus and is considered to be the most distant object yet detected in the universe. Quasars were first identified as being high redshift sources of electromagnetic energy, including radio waves and visible light, that were point-like, similar to stars, rather than extended sources similar to galaxies.

The word quasar is short for "quasi-stellar radio source". This name, which means star-like emitters of radio waves, was given in the 1960s when quasars were first detected. Despite their brightness, due to their great distance from Earth, no quasars can be seen with an unaided eye. Energy from quasars takes billions of years to reach the Earth's atmosphere.

There is now a scientific consensus that a quasar is a compact region 10-10,000 Schwarzschild radii across surrounding the central supermassive black hole of a galaxy, powered by its accretion disc. Quasars show a very high redshift, which is an effect of the expansion of the universe between the quasar and the Earth. When combined with Hubble's law, the implication of the redshift is that the quasars are very distant. The most luminous quasars radiate at a rate that can exceed the output of average galaxies, equivalent to one trillion (1012) suns.

The first quasars were discovered as radio loud sources in the late 1950's & early 1960's. The first optical discovery to accompany a radio source came in 1960 when radio source 3C 48 was tied to an optical object. The optical spectrum was difficult to interpret with many before unseen emission and absorbtion lines. In 1963 another source was tied with an optical component and it too exhibited these strange emission /absorbtion lines. It was soon discovered that these weren't so strange as they were just redshifted.