Devilish OMG particles
Tens of millions of times more energetic than particles produced by the most powerful human-made accelerators, ultra-high-energy cosmic rays are a mystery—there is no known phenomenon in the Universe that could create them. In 2007, the Pierre Auger Observatory, with detectors spread over 3,000 square kilometres of Argentina’s Pampas, seemed to be on its way to chasing down the source of these unholy monsters, sometimes nick-named ‘Oh-My-God’ particles. They found that the rays seemed to concentrate in 'hotspots' in the vicinity of particular galaxies, suggesting that they might originate in the overheated matter surrounding supermassive black holes at the galaxies' centres. But as the observatory accumulated more data, the link waned.
Just as the idea that there might be hotspots of OMG particles seemed left for dead, a fresh hotspot in the Northern Hemisphere was detected by a smaller, Japanese-led experiment in Utah called the Telescope Array. At this stage, the concentration is more phantom than fully-fledged zombie because its statistical significance is low. And the experiment sees only two or three events each year, so it could take some time to find a resolution. To speed things up, the collaboration plans to nearly quadruple the size of the array to fill about 2,500 square kilometres, a project expected to take three years.
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