'Extreme Universe' puzzle deepens (BBC)
By Jason Palmer
Science and technology reporter, BBC News
The mystery surrounding the source of the highest-energy particles known in the Universe has grown deeper.
The particles, known as cosmic rays, can show up with energies a million times higher than the biggest particle accelerators on Earth can produce.
Astrophysicists believed that only two sources could make them: supermassive black holes in active galaxies, or so-called gamma ray bursts.
A study in Nature has now all but ruled out gamma ray bursts as the cause.
Gamma ray bursts (GRBs) are the brightest events we know of, though their sources remain a matter of some debate. They can release in hours more energy than our Sun will ever produce.
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more: http://www.bbc.co.uk/news/science-environment-17768771
free abstract, $$$ full paper: http://www.nature.com/nature/journal/v484/n7394/full/nature11068.html
