Ultra-high-energy cosmic ray
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In high-energy physics, an ultra-high-energy cosmic ray (UHECR) is a cosmic ray (subatomic particle) which appears to have extreme kinetic energy, far beyond both its rest mass and energies typical of other cosmic rays. These particles are significant because they have energy comparable to (and sometimes exceeding) the Greisen-Zatsepin-Kuzmin limit.
The Oh-My-God particle (a play on the nickname "God particle" for the Higgs boson) is the nickname given to a particle observed on the evening of October 15, 1991, over Salt Lake City, Utah, estimated to have an energy of approximately 3 × 1020 electronvolts, equivalent to about 50 joules—in other words, it was a subatomic particle with macroscopic kinetic energy equal to that of a baseball (140 g) moving at about 27 m/s (60 mph).
It was most likely a proton travelling with velocity almost equal to the speed of light (if it was a proton, its speed would have been approximately (1 - (5 × 10-24)) c; after traveling one light year the particle would be only 46 nanometres behind a photon that left at the same time[1]) and its observation was a shock to astrophysicists.
Since the first observation, by the University of Utah's Fly's Eye Cosmic Ray Detector, at least fifteen similar events have been recorded, confirming the phenomenon. The source of such high energy particles remains a mystery, especially since interactions with blue-shifted cosmic microwave background radiation limit the distance that these particles can travel before losing energy (the Greisen-Zatsepin-Kuzmin limit).
Because of its energy the Oh-My-God particle would have experienced very little influence from cosmic electromagnetic and gravitational fields, and so its trajectory should be easily calculable. However, nothing of note was found in the estimated direction of its origin.
At a January 12, 2005 conference of the American Astronomical Society, particle physicist Glennys Farrar presented a paper tracing five similar very-high-energy cosmic rays, all of which were detected between 1993 and 2003, to a pair of colliding galaxy clusters 450 million light-years from Earth. Farrar speculated that the clusters' powerful magnetic fields could become warped in the collision, accelerating charged particles to the extreme energies astronomers have observed.
[edit] References
- ^ Walker, John (January 4 1994). The Oh-My-God Particle.
- R. Clay et al. (1999). Cosmic Bullets. Perseus Books. ISBN 0-7382-0139-1. - A good introduction to ultra-high energy cosmic rays.
[edit] See also
[edit] External links
- The Highest Energy Particle Ever Recorded The details of the event from the official site of the Fly's Eye detector.
- John Walker's lively analysis of the 1991 event, published in 1994
- Update: Science 2000 (subscription required). This references, probably, to Science 288(5469): 1147.
- Origin of energetic space particles pinpointed, by Mark Peplow for news@nature.com, published January 13, 2005.
