Pierre Auger Observatory

50 year-old mystery has been solved

Ever since the existence of cosmic rays with individual energies of several Joules was established in the 1960s, speculation has raged as to whether cosmic particles of mean energy of 2 Joules are created in our Milky Way or in distant extragalactic objects.

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Multi-resolution anisotropy studies of ultrahigh-energy cosmic rays detected at the Pierre Auger Observatory


Cosmic rays are mostly charged particles that  reach Earth from outer space. Although they were discovered more than a century ago, the origin of the ultra-high energy ones (with an energy above 1018 eV, or 100,000 times more energetic than the particles in the LHC beam, the most powerful particle accelerator on Earth) is still a puzzle. The large area of the Pierre Auger Observatory of about 3000 km2 compensates for the low flux of such particles and allows us to search for an excess/deficit of events arriving from different directions in the celestial sphere.

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Combined fit of spectrum and composition data as measured by the Pierre Auger Observatory


The Pierre Auger Collaboration has investigated the constraining power of the cosmic ray spectrum and composition measurements with respect to the properties of the possible sources.

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