Photograph by NASA/Swift/Aurore Simonnet
Gamma Ray Burst
THREAT: Gamma-ray bursts are the most powerful explosions in the Universe, beaming high-intensity radiation in the aftermath of a supernova. They are a million trillion times brighter than the Sun, according to NASA. "If one happened nearby," says Caltech theoretical physicist Sean M. Carroll, "the intense beam of gamma radiation could easily lead to a mass extinction event, or even destroy all life on Earth."
REALITY: All the gamma-ray bursts so far observed have been outside our Milky Way galaxy. The closest was 450 million light-years away. They are so rare that they shouldn't be a concern and so powerful that we wouldn't have time to react anyway.
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