A thin rain of charged particles continually bombards our atmosphere from outer space. The mysterious particles were first detected 100 years ago but until 10 years ago when a new type of telescope began to come online physicists weren't sure where the "cosmic rays" came from or how they were generated. They suspected the particles were accelerated by supernova shockwaves, but suspicions aren't proof.
Imaging atmospheric Cherenkov telescopes now keeping a watchful eye on the night skies are finally providing the evidence needed to solve this longstanding puzzle.
Full article on ScienceDaily