Rotating Supermassive Black Holes

Active galaxies and quasars appear to require a compact energy source of enormous strength. As we have seen, the most plausible candidate is a rotating, supermassive black hole of order a billion solar masses at their center (recall that normal stellar black holes probably contain only of order ten solar masses of matter). Until recently there has been strong circumstantial evidence to support such a mechanism. In the past few years evidence of much more direct nature has emerged.