A Quasar (contraction of QUASi-stellAR raio source) is an extremely powerful and distant active galactic nucleus. They 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. While there was initially some controversy over the nature of these objects, there is now a scientific consensus that a quasar is a compact region 10-10000 Schwarzschild radii across surrounding the central supermassive black hole of a galaxy.