Powerful Cosmic Rays: Not From the Neighborhood, Scientists Say

By Gabriel Gache, Science News Editor

March 25, Softpedia

More than 42 years ago, Kenneth Greisen from Cornell University, Grorgiy Zatsepin and Vadim Kuzmin from Mascow Lebedev Institute of Physics independently predicted that cosmic rays emitted throughout the universe would never hit the Earth at their full strength due to collision with the Cosmic Microwave Background, remnant of the Big Bang event that led to the birth of the universe. This is called Greisen-Zatsepin-Kuzmin (GZK) suppression of ultrahigh-energy cosmic rays.

Now, University of Utah's High-Resolution Fly's Eye cosmic ray observatory studies the GZK limit for energetic particles originating in remote areas of the universe. The basic idea is that cosmic rays pack energy much higher than the GZK limit during emission, however, while traveling through space, they lose a great deal of energy through CMB collision.

University of Utah College of Science professor Pierre Sokolsky, and leader of the study, reveals: "It has been the goal of much of ultrahigh-energy cosmic ray physics for
the past 40 years to find this cutoff or disprove it. For the first time in 40 years, that question is answered: there is a cutoff."

The High Resolution Fly's Eye cosmic ray observatory located in Utah's western desert conducted continuous observations on cosmic rays between 1997 and 2006, but the research was boosted by the Auger cosmic ray observatory which showed last year that the number of ultrahigh-energy cosmic rays that rain down on Earth and exceed the energies predicted by the GZK limit is rather small in comparison to high-energy cosmic rays.

The discoveries made by the Auger observatory and HiRes observatory clearly showed that the Akeno Giant Air Shower Array measurements were flawed since no GZK limit was detected. Data provided by the AGSA observatory revealed that cosmic rays ten times higher than the GZK limit are able to reach the Earth, thus contradicting the measurements made with Auger and HiRes.

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photo: Centaurus A galaxy seems to emit high energy cosmic rays from its active galactic nucleus (NASA)