Evidence for Rapidly Spinning Black Holes in Quasars

It has long been believed that accretion onto supermassive black holes powers quasars, but there are still relatively few observational constraints on the spins of the black holes. We address this problem by estimating the average radiative efficiencies of a large sample of quasars selected from the Sloan Digital Sky Survey, by combining their luminosity function and their black hole mass function. Over the redshift interval 0.4