Quasars or quasi-stellar radio sources are the most energetic and distant active galactic nuclei (AGN).
They are quite small in comparison with the energy they put out. Quasars are not much larger than the Solar System. The mechanism of brightness changes probably involves relativistic beaming of jets pointed nearly directly toward us. The highest redshift quasar known (as of June 2011[update]) has a redshift of 7.085, which means it is about 29 billion light-years from Earth. This estimate is made using the concept of comoving distance.