Unusual Bursts of Gamma Rays Leave Scientists Puzzled

A distant galaxy has showered Earth with two record-setting bursts of very high-energy gamma rays and dumped a puzzle into scientists’ laps. The bursts came from a galaxy called Markarian 421, about 400 million light-years away. The first burst, on May 7, sent 15 to 16 gamma rays per minute crashing into the Earth’s atmosphere, nearly three times the old record.

The second flare, eight days later, set a record for being so brief: half an hour. Previously observed flares have lasted for days. This brevity suggests that the gamma rays must have been generated within a very small space. “It’s very difficult to explain how this happened,” said physicist Jim Gaidos of Purdue University, who discussed the bursts in the Sept. 26 edition of Nature. Scientists will now have to rethink their theories to come up with a way that a galaxy could produce the high intensity seen in the first burst, through some process that can turn on and off in only half an hour, and act within a very small space, Gaidos said.