Gamma-ray burst may have struck Earth during Middle Ages

BBC : From the presence of radioactive carbon in ancient Japanese cedar trees and radioactive beryllium in Antarctic ice, scientists believe that a blast of radiation struck Earth around AD 774â775. Several theories have been put forth as the source, including a supernova or a solar flare. However, Ralph Neuhäuser of the University of Jena in Germany and colleagues have recently published a paper in the Monthly Notices of the Royal Astronomical Society in which they propose that the wave of radiation was produced by a gamma-ray burst (GRB) within the Milky Way. “We looked in the spectra of short gamma-ray bursts to estimate whether this would be consistent with the production rate of carbon-14 and beryllium-10 that we observedâmdash;and [we found] that is fully consistent,” said Neuhäuser. Because no extinction event was triggered, the GRB must have occurred sufficiently far away, some 3000 to 12 000 light-years. In galaxies like the Milky Way, GRBs are expected to occur just once every 100,000 to 1 million years. It is therefore “extremely unlikely” that Earth would experience another anytime soon, according to Neuhäuser.