If ancient mariners were mapping the universe, the gamma ray fog that fills the cosmos would now be marked with a warning: Here be dragons.

That's the conclusion of a new study of the fog, which found that the source of the high-energy radiation is even more of a mystery than anticipated.

Previously, scientists had surmised that most if not all of the fog's gamma rays are being created by powerful galaxies with active supermassive black holes at their hearts.

Active black holes spew jets of particles traveling at nearly the speed of light. When these high-speed particles slam into ambient gases, gamma rays are born and go zipping in all directions through interstellar space.

But