Their existence was first reported in studies appearing in the March 16, 1963, edition of the journal Nature. The photo shows quasar 3c 273 at the center.
* "3c 273: A star-like object with large red-shift" (Maarten Schmidt, Nature, March 16, 1963): @
* Definition from "Firefly Astronomy Dictionary" (2003): @
* Entry from NASA's Chandra X-Ray Center: @