Did a Gamma Ray Burst Irradiate Earth in the 8th Century?
In 2012 scientist Fusa Miyake announced the detection of high levels of the isotopes Carbon-14 and Beryllium-10 in tree rings formed in 775 CE, suggesting that a burst of radiation struck the Earth in the year 774 or 775. These isotopes form when radiation from space collides with nitrogen atoms, which then decay into these heavier forms of carbon and beryllium.
A nearby supernova was ruled out as the cause of the burst, as no observations were recorded at this time, aside from a possible sighting in 776 CE, which was too late to account for the C-14 data. Miyake also ruled out solar flares because they are not powerful enough to account for the observed excess of C-14.
Astronomers Valeri Hambaryan and Ralph Neuhӓuser of the Astrophysics Institute of the University of Jena in Germany may have a better answer: a nearby short duration gamma burst. They suggest that two compact stellar remnants (black holes, white dwarfs or neutron stars) collided together, releasing a gamma ray burst. In these mergers the burst is short and intense, lasting less than two seconds. This explanation would be consistent with both the C-14 measurements and the absence of any recorded events in the sky. The merging stars could not have been closer than 3,000 light years away, of the burst would have led to the extinction of some terrestrial life. Hambaryan and Neuhӓuser believe the gamma ray burst originated 3,000 - 12,000 light years from the Sun.
-JF
Image: artist's impression of the merger of two neutron stars (Credit: NASA/Dana Berry) Larger image: http://www.ras.org.uk/images/stories/press/114914main_neutcollidecloseup_strip.jpg Sources: http://www.sciencedaily.com/releases/2013/01/130121083255.htm http://www.ras.org.uk/news-and-press/224-news-2013/2215-did-an-8th-century-gamma-ray-burst-irradiate-the-earth