"A huge explosion halfway across the galaxy packed so much power it briefly altered Earth's upper atmosphere, astronomers said Friday. No known eruption beyond our solar system has ever appeared as bright upon arrival."
"The blast originated about 50,000 light-years away and was detected Dec. 27. A light-year is the distance light travels in a year, about 6 trillion miles (10 trillion kilometers). "Had this happened within 10 light-years of us, it would have severely damaged our atmosphere and possibly have triggered a mass extinction," said Bryan Gaensler of the Harvard-Smithsonian Center for Astrophysics (CfA)." Full Story  on Space.com.