Gamma ray hide & seek

May 14, 2000

Draping the earth and entire universe in a thin, ever-present veil, their origin remains one of the greatest puzzles of cosmology. However, the mystique of gamma rays -- particles of light comprising the most energetic and penetrating form of electromagnetic radiation -- may soon diminish thanks to research by Dr. Eli Waxman of the Weizmann Institute's Condensed Matter Physics Department together with Prof. Abraham Loeb of the Harvard-Smithsonian Center for Astrophysics.

Their study, reported in the May 11 issue of Nature, suggests that most of the gamma radiation reaching the earth may actually be leftover energy from massive shock waves induced by gravitational forces. Operating on intergalactic clouds of gas, these forces caused them to collapse into themselves, creating giant galactic clusters. This process produced electrons moving at nearly the speed of light -- roughly 185,000 miles per second. The electrons then collided with low energy photons of the "cosmic microwave background radiation," which is believed to be an "echo" of the Big Bang (the point in time billions of years ago when the universe was created in a cosmic explosion). The collision scattered the photons and increased the energy of a fraction of them to that of gamma rays, thus producing the gamma-ray background radiation seen in today's universe.

The model proposed by Waxman and Loeb, which is consistent with the theory of particle development following the Big Bang, may shed light on the amount of gaseous material currently captured within intergalactic clouds, thereby unraveling another longstanding astrophysical mystery -- that of "missing matter." According to the Big Bang theory, the amount of ordinary matter (as opposed to "dark matter," which is invisible since it does not emit light) in the universe is much larger than that observed in stars and galaxies. Most of the ordinary matter in the universe may therefore be captured within intergalactic clouds, and the observed gamma-ray photons may be the first signature of its existence.

The model and its findings will be examined in upcoming years via an American research satellite probing gamma radiation throughout the universe, as well as a series of earth-based radio wave sensors.
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Dr. Eli Waxman's research is supported by the Joseph H. and Belle R. Braun Center for Submicron Research.




American Committee for the Weizmann Institute of Science

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