... Behemoth black hole found in an unlikely place . ... Quasars powered by black holes . Astronomers believe that variability in quasars' light output is tied to the mass of black holes at their centers. ... Using data obtained by the Sloan Digital Sky Survey, the researchers monitored the brightness and estimated the central black hole mass of more than 2,500 quasars, observed over a period of four years. ... Only registered members of Astronomy.com are allowed to comment on this article. ...