The recently completed Pierre Auger cosmic-ray observatory in Argentina covers 3000 km2 with ground detectors and fluorescence telescopes. Its purpose is to determine the distribution in energy, composition, and arrival direction of extragalactic cosmic rays with energies above 1018 eV. Seeking evidence of what accelerates cosmic rays to ultrahigh energies, two groups have reported searches for correlations between the directions of the 27 highest-energy cosmic-ray events reported by Auger last year and the locations of candidate source galaxies (see Physics Today, Physics Today 0031-9228 611200816 https://doi.org/10.1063/1.2835138 January 2008, page 16 ). Matthew George (University of Cambridge) and coworkers have found a strong correlation between the arrival directions and the positions of active galactic nuclei closer than 300 million light-years with particularly intense hard x-ray output. The other correlation study, by Gabriele Ghisellini (Brera Astronomical Observatory, Merate, Italy) and coworkers, found a strong correlation between...

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