Particles of the highest known energies (up to about 50 Joules per particle) are emitted by astronomical objects which, even by today's astronomical standards are considered exotic ones: active galactic nuclei, perhaps gamma ray bursters, etc. [For comparison, note that when a tennis champion hits a very hard serve, the initial kinetic energy of the tennis ball is about 10 Joules; however, for cosmic ray particles, this energy is concentrated on a particle of mass 10^(-27) kg or less!] Terrestrial accelerators (even the future Large Hadronic Collider under construction in Geneva, Switzerland) produce particles of energies which are of many orders of magnitude smaller.
One has to pay a price for investigating particles of the highest energies: very few of them hit the Earth. Their observation requires special detectors. Some of them, like the antarctic detector AMANDA, MACRO or Super Kamiokande are presently collecting data. Several others, like NESTOR , or the Pierre Auger Project are still at the stage of development: they will start data taking within a few years.
High energy astroparticle physics is an exciting and rapidly developing discipline! It involves some unusual astrophysics and the leading edge of particle physics known today. It may easily lead to the next breakthrough in high energy particle physics and a much better understanding of those "exotic" objects in the sky giving rise to the highest energy particles.
If you are interested, sample some of our publications. (This is continuously updated.) Further questions or comments? send an e-mail message: we shall respond SOON!
(Last update of this file: September 11, 2000)