Quasars, or quasi-stellar objects, have long been a puzzle to astronomers. They were originally assumed to be normal stars in our own galaxy with a larger than normal emission of radio waves. When seen through ground-based telescopes, these compact, enigmatic light sources resemble stars, yet we now know that they are billions of light-years away and several hundred billion times brighter than normal stars—their output of light and radio waves can equal that of 100 whole galaxies. Astronomers believe that a quasar turns on when a massive black hole at the nucleus of a galaxy feeds on gas and stars. As the matter falls into the black hole, intense radiation is emitted. Eventually, the black hole will stop emitting radiation once it consumes all nearby matter. Then it needs debris from a collision of galaxies or another process to provide more fuel.

Quasar in Elliptical Galaxy M87, Chandra, courtesy NASA/ESA/MIT