Astronomers are closer to finding the source of short enigmatic bursts of radio waves coming from deep space—one of the most puzzling astronomical phenomena to emerge in recent years. Researchers found the first fast radio burst (FRB) 10 years ago, and have since found a handful of others. They initially thought the blasts, lasting just a few milliseconds, came from some cataclysmic event such as the merger of two neutron stars—superdense stellar remnants—to form a black hole. But the discovery in 2012 of an FRB that repeats at regular intervals, dubbed FRB 121102, suggests that whatever is causing this particular FRB is not destroyed in the process. Last year, a team reported pinpointing the location of FRB 121102 to a small galaxy 3 billion light-years away, suggesting a powerful source to be detectable from so far but, puzzlingly, coming from a small galaxy—an unlikely home for heavyweight events. Now, a team using the Arecibo radio telescope in Puerto Rico has discovered that the polarization of the bursts’ radio waves—the direction in which the waves vibrate—rotates in a fast and unpredictable way. This suggests, they report today in Nature, that the bursts come from somewhere very hot and with a very high magnetic field. Such conditions exist, they say, around a massive black hole (like the one above), and the short duration of the pulses suggests they come from something small, like a neutron star. A neutron star orbiting a black hole then? Maybe, the team concludes, but some other proposed FRB models, like magnetized gas clouds or supernova remnants, could also explain the weird polarization. So no explanation for FRBs yet, but this one seems to live somewhere pretty extreme.