quasarastronomy

any of a class of rare cosmic objects of high luminosity that often have strong radio emission that is observed at great distances. These objects are also called QSOs, which stands for “quasi-stellar objects.”

The bright emitting regions of quasars are no more than a light-year or two in size, but they are up to 1,000 times more luminous than giant galaxies, which can have a diameter of 100,000 light-years. The tremendous brilliance of quasars allows them to be observed at distances of more than 10,000,000,000 light-years. This enormous amount of radiation is released from a small area at the centre of what appears to be a normal galaxy. Some evidence suggests that the galaxy is experiencing a tidal encounter with another galaxy. Most investigators attribute such energy generation to gas spiraling at high velocity into a massive black hole. An outer atmosphere of tenuous gas produces emission lines that are observed in the spectra of quasars. These emission lines are always shifted toward the red, corresponding to large Doppler velocities of recession. According to Hubble’s law of the expansion of the universe, these large velocities correspond to large distances. Quasars were more numerous about 10 billion years ago than they are at present. The brightest quasar in the sky is 3C 273, which lies at a distance of 2,000,000,000 light-years from the Earth. Radio interferometry shows that the radio nucleus of 3C 273 is emitting jets of ionized gas that are expanding at nearly the velocity of light.