Twenty years of ultra-high-energy cosmic-ray physics with the Pierre Auger Observatory

Since the discovery of the first cosmic particle with an energy of about 1020 eV, more than one Joule, in the 1960ies, understanding the origin and nature of these particles has been a central goal in astro- and particle physics. The extremely small flux of these particles, which can only be observed indirectly through their gigantic cascades of secondary particles they produce when entering the Earth’s atmosphere, has made progress in this field very difficult. With the Pierre Auger Observatory, an detector installation covering an area of 3000 km2 in Argentina, the so-far largest number of these particles has been detected in unprecedented quality. The Auger Observatory began taking data in 2004 and has since revolutionized our understanding of ultra-high energy cosmic rays. In this talk, we will review the main results of the Auger Observatory and discuss their implications in the context of astroparticle physics.