For decades, physicists have sought the sources of the most energetic subatomic particles in the universe-cosmic rays that strike the atmosphere with as much energy as well-thrown baseballs.
The observation suggests the cosmic rays emanate from a distinct source near our galaxy and not from sources spread all over the universe. The Telescope Array team has taken a more catholic approach, looking only for evidence that cosmic rays do not arrive in equal numbers in all directions. When a high-energy cosmic array strikes the atmosphere, it disappears in an avalanche of lower energy particles. Those particles trigger the detectors in the array, enabling researchers to deduce the direction and energy of the original cosmic ray. If the Telescope Array is starting to see a source of ultra-high-energy cosmic rays, then its identity remains unclear.
Physicists think that the highest energy cosmic rays cannot come from more than 500 million light-years away, as interactions with lingering radiation from the big bang ought to snuff out cosmic rays from more distant sources.