A team of scientists has determined that Earth was hit by a massive gamma ray burst—the most powerful explosion known in the Universe—all the way back in AD 775.
Last year, researchers discovered ancient cedar trees in Japan that contained unusual levels of radioactive carbon-14, as well as spikes of beryllium-10 in Antarctic ice. By analyzing the tree rings and using ice-core data, the researchers pinned the presence of both sets of radiation to the years AD 774 and AD 775.
These kinds of radioactive isotopes are created when intense radiation hits atoms in the upper atmosphere of our planet. Now, the BBC reports, scientists suggest that they are a result of a massive gamma-ray burst which hit the planet during Medieval times. Professor Ralph Neuhauser, from the Institute of Astrophysics at the University of Jena, explains:
"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 observed - and [we found] that is fully consistent.... Gamma-ray bursts are very, very explosive and energetic events, and so we considered from the energy what would be the distance given the energy observed. Our conclusion was it was 3,000 to 12,000 light-years away - and this is within our galaxy."
Such a burst sounds dramatic, and it has certainly left an enduring impact, but our medieval ancestors might not have noticed it: most of the radiation would have been absorbed by the atmosphere and then made its way to the planet's surface over a long period of time. Sadly, there would have been no blinding flash of intense visible light to signal the burst, either—but it's amazing to find out that a once-in-a-million-years event shook the planet so recently. [BBC]
Image by ESA