An Etymological Dictionary of Astronomy and Astrophysics

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فرهنگ ریشه‌شناختی اخترشناسی-اخترفیزیک

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UHECR puzzle
  چیستان ِ پرتوهای ِ کیهانی ِ اولتر-مه-کاروژ  
cistân-e partowhâ-ye keyhâni-ye ultar-meh-kâruž
Fr.: énigme des rayons cosmiques de très haute énergie  

The question of the origin and nature of the → ultra high energy cosmic rays.
According to the → GZK cutoff, the UHECRs should be nearby. They are expected to be exceptional, therefore visible by some astrophysical counterpart. However, there is nothing visible (within a few tens of → Mpc) in the direction of all the UHECR detected up to now.

See also: → UHECR; → puzzle.