Gamma rays and black holes

Scientists do not know what causes massive explosions that cause huge amount of gamma rays to be released. Scientists keep finding more evidence and ideas.

Astronomers have discovered a gamma ray source in the sky that acts like a natural clock. The object is called LS 5039, and consists of a massive blue star orbiting an unknown object - possibly a black hole. The two objects orbit each other closely, completing an orbit every four days. With each orbit, the black hole flies through the blue star's stellar wind, and accelerates particles to gamma ray levels. This is the first time a source of gamma rays has been discovered with such a regular schedule.

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http://www.universetoday.com/2006/11/28/set-your-clock-with-gamma-rays/