The origin of ultra-high energy cosmic rays (UHECRs), cosmic rays with energies above 10^{19} eV, is still a mystery. In this talk, I will review this phenomena and explain the basic physics involved in its study. I will then present the recent results of the AUGER experiment, and discuss their implications. In the last part, I will describe the recent idea of radio-quiet active galactic nuclei (AGNs) as possible sources of UHECRs.
Reference:
Pe'er & Murase & Meszaros 2009, PRD, 80, 123018
