Dramatic Hubble telescope pictures reveal that quasars live in a remarkable assortment of galaxies, many of which are violently colliding. This complicated picture suggests there may be a variety of mechanisms — some quite subtle — for "turning on" quasars, the universe's most energetic objects. When seen through ground-based telescopes, these compact, enigmatic light sources resemble stars, yet they are billions of light-years away and several hundred billion times brighter than normal stars.

These Hubble snapshots offer examples of quasar home sites. Astronomers believe that a quasar turns on when a massive black hole at the center of a galaxy feeds on gas and stars.

Photo credit: NASA/John Bahcall (Institute for Advanced Study, Princeton), Mike Disney (University of Wales)