Researchers find gamma ray origins

By Deborah Rafferty

The Incredible Hulk would love the M82 galaxy8212;it’s where a huge amount of the gamma rays that created him are coming from, according to U scientists.

U researchers participated in an international study using the Very Energetic Radiation Imaging Telescope Array System, a ground-based gamma-ray observatory in Tucson, Ariz. Researchers who participated in the study detected high-energy gamma rays emitting from the starburst galaxy M82. The study was published in the online edition of Nature on Sunday.

Before this discovery, scientists had no conclusive evidence of where these cosmic rays were originating. They had been looking for the source but were unable to point to a spot and say for certain if any specific patch of space was the cause of these high-energy gamma rays, said David Kieda, U professor and chairman of the department of physics.

“This means we understand where cosmic rays are coming from,” Kieda said. The international study was led by the Harvard Smithsonian and involved 20 universities from around the world. The U had several undergraduate and graduate students spend time this summer working on this discovery at the VERITAS center.

This discovery supports a previously suggested connection that supernovas play a significant role in the creation of cosmic rays, Kieda said.

The scientists used the VERITAS to study the M82 galaxy. Located 12 million light-years away, it is a starburst galaxy that has numerous supernovas exploding within a short amount of time.

It is not normal for a galaxy to have this many star bursts in a relatively small amount of time, Kieda said. In comparison to the Milky Way galaxy, in which a supernova goes off about once every 100 years, the M82 galaxy is experiencing about one supernova explosion every year, Kieda said.

“The M82 galaxy has a lot of supernovas going off,” Kieda said. “So many star bursts make a wave of gamma rays that we can observe. This is the first time anyone has seen this happen.”

The frequency of supernova explosions makes the M82 galaxy a good location to look for the origins of cosmic rays. When a supernova goes off, it creates a spectacular explosion that emits a visible expanding shock wave of gamma rays, Kieda said.

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