A quasar is one of the brightest and oldest objects in the universe. The majority of quasars existed around when the universe was half its present size. Quasars are simply huge black holes, which produce immense amounts of light and other radiation as discs of material, known as accretion disks, flow into it.
At the last astronomy colloquia, professor Paul Martini of the Harvard-Smithsonian Centre for Astrophysics, explained that it is now thought that quasars can “turn off and on” during their lifetime, depending on whether enough material is flowing in to allow it to produce radiation above a certain threshold.
It is thought that many of the present galaxies, which are all believed to contain huge black holes at their center, may have been quasars in the far past which have now turned off. Our own Milky Way galaxy, for example, may have itself been a bright quasar some 10 billion years ago as it grew to its present size. The study of quasars is of immense importance because their birth and growth can be correlated with the birth and growth of the galaxy of which they are a part.
Martini’s research further predicts a correlation between the lifetime of a quasar and the number of these objects in the universe. The idea is that if each quasar is on for a shorter amount of time, there must be more of them on at any one time to account for the overall brightness produced.
