Professor Glennys R. Farrar, a physicist at New York University, today announced that, for the first time, a source of ultra-high energy cosmic rays has been isolated and studied, a major breakthrough in the field. Ultra-high energy cosmic rays--which rarely hit the earth--are believed to be the result of extremely powerful cosmic phenomena, such as the creation or accretion of massive black holes. In addition to elucidating the origin of these remarkable particles and the systems that create them, the findings also shed light on the nature of very large scale magnetic fields, which are suspected to permeate space between galaxies. The announcement was made in a report to the American Astronomical Society meeting in San Diego, California.
The result was made possible by applying a new analysis technique to data from two different observational teams using distinct approaches to finding and measuring powerful cosmic rays. The analysis will enable physicists to explore in a sustained and focused fashion how such energetic particles are produced.
The data upon which this work is based were obtained by the Akeno Giant Air Shower Array (AGASA) experimental collaboration in Japan and the National Science Foundations High Resolution Flys Eye Air Fluorescence Detector (HiRes) collaboration in Utah. The hints of possible clusters of cosmic ray occurrences detected by AGASA and HiRes individually were each too weak to be statistically convincing, and previous analysis methods were unsuitable for studying the combined dataset. In a paper in press (Astrophysical Journal), Farrar and the HiRes collaboration used the "method of maximum likelihood" to analyze the combined AGASA and HiRes datasets, revealing a tightly clustered group of four ultra-high energy events from one segment of the sky. The probability that such a well-correlated cluster of particles arises simply by coincidence is calculated to be a less than one in a hundred. Nevertheless, the authors caution that such coincidences do happen and note that a posteriori probability estimates are hazardous, so stress that more data are needed before firm conclusions can be drawn.
James Devitt | EurekAlert!
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