Massive black hole binaries in active galactic nuclei

Most theoretical discussions of active galactic nuclei (including quasars) attribute their energy production either to an accreting black hole or to a precursor stage-for instance a dense star cluster or a supermassive star-whose inevitable end point is a massive black hole¹. We explore here the possibility that some active nuclei may contain two massive black holes in orbit about each other. This hypothesis suggests a new interpretation for the observed bending² and apparent precession³ of radio jets emerging from these objects and may indeed be verified through detection of the direct consequences of orbital motion.