At the end of 2017, a galaxy 236 million light years away began a rare and dramatic transformation. Its an event astronomers are still puzzling over, one set off by changes near its central black hole. They first explained this as a title disruption event. That's when a star wanders so close to a supermassive black hole that it's torn apart. A new study of observations spanning the entire event suggests a different cause. The trigger may have been a flip in the magnetic field in the disc of material around the black hole. The Sun's magnetic field reverses polarity every 11 years. On longer time scales, even Earth's magnetic field flips. Starting in December 2017, the galaxy began to brighten invisible and ultraviolet light. The source of this brightening appeared to be the disc of material around the black hole.