Centre national de la recherche scientifique
The largest detector of cosmic rays in the world, the Pierre Auger observatory, was inaugurated on November 14th and 15th 2008 in Argentina. Catherine Bréchignac, CNRS president, was present at the ceremony.
This observatory, which is born of a collaboration between 17 countries, including France, was built to solve one of the greatest enigmas in astrophysics: the origin and nature of ultra high energy cosmic rays, with energies which can exceed hundreds of billions of electronvolts (eV).
Even though the last part of the installation in the Andes, where work began in 1999, has just been completed, the cutting edge detector has already produced precious results, published in Science in 2007. The observatory has detected 27 events with energy above the limit known as « GZK » 1. In the direction of practically each one of these events, an active galaxy was found closer than 300 million light-years from Earth, in other words in the neighborhood of our galaxy. This suggests that most cosmic rays originate from nearby astronomical sources of this type. And this in turn suggests that the particles are probably protons or iron nuclei.
One of the telescopes of the observatory which is connected to 1600 surface detectors. © Observatoire Pierre Auger
1. Limit of 60.1018 eV, an energy level that cosmic ray particles can theoretically not exceed if they travel more than 500 million light-years.
