Roughly every 114 days, almost like clockwork, a galaxy 570 million light-years away lights up like a firework. Since at least 2014, our observatories have recorded this strange behaviour; now, astronomers have put the pieces together to figure out why. In the centre of the spiral galaxy, named ESO 253-G003, a supermassive black hole is being orbited by a star that, every 114 days, swings close