Giant black holes play to Einstein's tune

OJ 287 is the active core of a galaxy some 3.5 billion light-years from Earth. At this core are a couple of black holes. One is a true colossus - a hole weighing 18 billion times the mass of our Sun; the other not quite so big at "only" 150 million Sun masses. The latter orbits the former in a predictable fashion, causing the system to flare up twice in every 12-year period. This animation shows how the orbit works. (Credit: R.Hurt/Abhimanyu.S)