An international research team led by Silke Britzen from the Max Planck Institute for Radio Astronomy in Bonn, Germany, has investigated blazars, accreting supermassive black holes in the centers of galaxies. Blazars show up when one of the emitted jets in the active galactic nucleus is pointing directly towards the Earth. The researchers present evidence that it is in fact the precession of the jet source, either caused by the presence of a second massive black hole close to the primary one or a warped accretion disk around a single black hole, that is responsible for the observed variability in blazars.
essentially predicta-ble, as it can be understood in geometrical terms (Fig. 2 and link