Observation of a large-scale anisotropy in the arrival directions of cosmic rays above 8 × 1018 eV

Pierre Auger Collaboration

Research output: Contribution to journalArticle

92 Scopus citations


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 3 × 104 cosmic rays with energies above 8 × 1018 electron volts, recorded with the Pierre Auger Observatory from a total exposure of 76,800 km2 sr year, we determined the existence of anisotropy in arrival directions. The anisotropy, detected at more than a 5.2σ level of significance, can be described by a dipole with an amplitude of 6.5+1.3 -0.9 percent toward right ascension αd = 100 ± 10 degrees and declination δd = -24+12 -13 degrees. That direction indicates an extragalactic origin for these ultrahighenergy particles.

Original languageEnglish (US)
Pages (from-to)1266-1270
Number of pages5
Issue number6357
StatePublished - Sep 22 2017


All Science Journal Classification (ASJC) codes

  • General

Cite this