Cosmic rays, the high energy protons and helium nuclei that constantly bombard the Earth, have puzzled astronomers for the best part of one hundred years. Where do they come from and how are they accelerated to energies in excess of 10^20 eV—that’s about the energy that Roger Federer gives a tennis ball during a serve? (By contrast, the Large Hadron Collider will be able to accelerate protons to a mere 10^12 eV.)
To tackle these questions, astronomers have built a giant cosmic ray telescope about the size of Rhode Island in Argentina. It’s called the Pierre Auger telescope and in the short time it has been operating, it is already challenging astronomers’ views about the origin of cosmic rays. In particular, it’s beginning to look as if the highest energy comsic rays come from active galactic nuclei.
Serguei Vorobiov from University of Nova Gorica in Slovenia summarises the highlights. Worth a read if you want to get up to speed on a new generation of astronomy.
Ref: arxiv.org/abs/0811.0752: The Pierre Auger Observatory — a New Stage in the Study of the Ultra-High Energy Cosmic Rays