Bulk Source of Universe's Gamma Rays Identified, Scientists Say

Scientists at Columbia University and Barnard College have found that the majority of the gamma rays outside of our galaxy are likely emitted by galaxy clusters and other massive structures. This may resolve a 30-year-old mystery as to the origin of the Universe's gamma-ray background.

The finding may also provide new insight about how structure formed in the Universe, as well as the nature of magnetic fields in the intergalactic medium, of which little is currently known.

Caleb Scharf of Columbia University and Reshmi Mukherjee of Barnard College publish this result in an upcoming issue of the Astrophysica Journal. The finding is based on the analysis of a nine-year record of gamma rays arriving at Earth from deep space, collected by NASA's Compton Gamma Ray Observatory throughout the 1990s.

For more on the discovery of galaxy clusters, go to: http://www.gsfc.nasa.gov/topstory/20020812gamma.html