Since their discovery in 1963, astronomers have been trying to crack the mystery of how these compact dynamos of light, which lie at the outer reaches of the universe, produce so much energy.
Quasars are no larger than our Solar System, but outshine galaxies of hundreds of billions of stars.
These light beacons have left trails of evidence and plenty of clues, but scientists have only just begun to understand their behavior. For centuries, quasars went undetected, appearing in the sky as faint stars. No one suspected anything more. In the 1940s, however, radio scientists discovered that celestial objects emitted radio waves, giving birth to radio astronomy. Soon astronomers began examining the sky to find as many objects as possible that radiated radio waves and tried to link them to optical objects.