Science & Tech

Gamma-ray astronomers detect “extreme” galaxies

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May signal new constituent of the cosmos

Gamma rays from X-ray emitting galaxies seem to signal the existence of what astronomers are calling “extreme” galaxies. An international team of astrophysicists made the discovery of very-high-energy gamma rays, confirming the hypothesis of an Italian group that galaxies which emit strongly in the highest energy X-rays would also emit the most energetic gamma rays. The first of these galaxies, Markarian 501, was detected in 1996. This detection was confirmed by several other observatories during a dramatic outburst in 1997. The second such galaxy, 1ES2344+514, gave hints of its nature during observations in 1998, but was not confirmed until recent months. The conventional explanation for these gamma-ray galaxies, dubbed “extreme” by Italian theorists at the Osservatorio Astronomico di Brera in Milan, is that the high energy emissions arise in jets of high energy particles originating in the vicinity of supermassive black holes.