<P> Quasars are found over a very broad range of distances (corresponding to redshifts ranging from z <0.1 for the nearest quasars to z> 7 for the most distant known quasars), and quasar discovery surveys have demonstrated that quasar activity was more common in the distant past . The peak epoch of quasar activity in the Universe corresponds to redshifts around 2, or approximately 10 billion years ago . As of 2017, the most distant known quasar is ULAS J1342 + 0928 at redshift z = 7.54; light observed from this quasar was emitted when the Universe was only 690 million years old . The supermassive black hole in this quasar is the most distant black hole identified to date, and is estimated to have a mass that is 800 million times the mass of our Sun . </P> <P> The term "quasar" was coined by Chinese - born U.S. astrophysicist Hong - Yee Chiu in May 1964, in Physics Today, to describe certain astronomically - puzzling objects: </P> <P> So far, the clumsily long name' quasi-stellar radio sources' is used to describe these objects . Because the nature of these objects is entirely unknown, it is hard to prepare a short, appropriate nomenclature for them so that their essential properties are obvious from their name . For convenience, the abbreviated form' quasar' will be used throughout this paper . </P> <P> Between 1917 and 1922, it became clear from work by Heber Curtis, Ernst Öpik and others, that some objects ("nebulae") seen by astronomers were in fact distant galaxies like our own . But when radio astronomy commenced in the 1950s, astronomers detected, among the galaxies, a small number of anomalous objects with properties that defied explanation . </P>

Where does the energy emitted by agn and quasars come from