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\u2014that\u2019s about the energy that Roger Federer gives a tennis ball during a serve? (By contrast, the\u00a0 Large Hadron Collider will be able to accelerate protons to a mere\u00a0 10^12 eV.)<\/p>\n
To tackle these questions, astronomers have built a giant cosmic ray telescope about the size of Rhode Island in Argentina. It\u2019s called the Pierre Auger telescope and in the short time it has been operating, it is already challenging astronomers\u2019 views about the origin of cosmic rays. In particular, it\u2019s beginning to look as if the highest energy comsic rays come from active galactic nuclei.<\/p>\n
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.<\/p>\n