Por Lorenzo Cazón (LIP).

Cosmic rays are atomic nuclei arriving from outer space that reach the highest energies observed in nature. Clues to their origin come from studying the distribution of their arrival directions. Using 3E4 cosmic rays above 8E18 eV recorded with the Pierre Auger Observatory, from a total exposure of 76,800 km2 sr yr, we report an anisotropy in the arrival directions. The anisotropy, detected at more than the 5.2 level of significance, can be described σ by a dipole with an amplitude of 6.5 ! towards right ascension α=100±10° and declination δ=−24±13°. That direction indicates an extragalactic origin for these ultra-high energy particles.