Something in space has been lighting up every 20 minutes since 1988

GPM J1839–10 was discovered in a search of the galactic plane for transient objects—something that's not there when you first look, but appears the next time you check. The typical explanation for a transient object is something like a supernova, where a major event gives something an immense boost in brightness. They're found at the radio end of the spectrum—fast radio bursts—but are also very brief, and so fairly difficult to spot.