When seen through ground-based telescopes, quasars are compact, mysterious light sources that resemble stars, yet they are billions of light-years away and several hundred billion times brighter than the average star. Some of these objects can emit the energy output of 10 billion suns. Given the incredible energy output, astronomers believe that quasars, which is short for quasi-stellar radio sources, turn on when a massive black hole at the center 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. These Hubble images show different quasar homes, which range from normal to highly disturbed galaxies. The top left image, for example, is of a normal spiral galaxy, while the bottom right depicts the merger of two galaxies. Both quasars are more than a billion light-years from Earth.