OJ287

Also known as the Sillanpää Quasar, OJ287 is a distant quasar that erupts once every 12 years. It is theorized this is caused by two orbiting supermassive black holes, the smaller one of which flies through the gigantic accretion disk of the larger one once in every 12 year orbit. The amount of energy released is comparable to billions of stars suddenly turning on and off.