Radiation from cosmic blast hit Earth in AD 774

A massive cosmic explosion in deep space sent out a pulse of high-energy radiation that hit the Earth in AD 774 and 775 when Charlemagne ruled much of Western Europe, scientists have found.

"Over the past 3,000 years this was the most energetic event to have hit the Earth," said Professor Ralph Neuhauser of the University of Jena in Germany. Last year, scientists discovered rings in Japanese cedar trees that had much higher levels of radioactive carbon 14 than normal for the period. Professor Neuhauser believes the radiation came from a collision either between two black holes or two stars between 3,000 and 12,000 light years away.