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Did a gamma-ray burst almost destroy Earth in the 8th century?

It’s the most powerful explosion in the known universe, and now scientists are saying Earth took the full brunt of a gamma-ray burst in the 8th century.

According to a newly published report, Earth was on the receiving end of a massive gamma-ray burst that left its mark across the globe.

Working in 2012, researchers reportedly discovered evidence that our planet was struck by a blast of radiation during the Middle Ages, which they now say was the result of either a pair of colliding black holes, or something similar.

A team of Britain’s Royal Astronomical Society researchers announced the finding on Monday, saying recent research seems to point to a gamma-ray burst, rather than a supernova or a massive solar flare ejected by the Sun. Previous research conducted by U.S. physicists suggested an unusually large solar flare from the Sun as the cause, or a massive supernova.

However, recent research points to a highly unusual event as the cause.  Working with tree rings and ice-core data, researchers said levels of carbon-14 concentrations were far higher than those present during a supernova or solar flares. According to researchers, carbon-14 concentrations in tree rings can be used as an indicator of cosmic-ray activity. Carbon-14 is produced by the interaction of atmospheric nitrogen with cosmic-ray neutrons.

Researchers say a high-resolution analysis of the carbon-14 content of annual rings in two Japanese cedar trees reveals evidence of an increase of carbon-14 content between AD 774 and AD  775, about twenty times larger than that expected as a result of ordinary solar modulation. The levels closely represent the energy levels associated with gamma-ray bursts, leading scientists to conclude that a short, two-second gamma ray burst struck Earth. Astronomers estimated that the blast occurred around 3,000 and 12,000 light years from the Sun.

While the event sounds disastrous  the same team noted that our ancient ancestors likely did not notice any difference. Earth’s atmosphere would have absorbed much of the radiation, leaving Earthlings with little to fear. However, a gamma-ray burst occurring closer to Earth — say a few hundred light years — would leave Earth in dire straits. According to astronomers, a gamma-ray burst just 200 light-years away would destroy our ozone layer, with devastating effects for life on Earth.

That said, gamma-ray bursts are extremely rare. Gamma-ray bursts can span from a small distance to billions of light-years across. Astronomers have observed a number of bursts, although astronomers do not yet have the ability to predict them.  Most blasts are billions of light years away from our planet, and they are also quite rare as only a few occur every one million years or so.

The cause of gamma-ray bursts can also be the result of a collision of neutron stars or white dwarf stars. Mergers of this kind are often observed, although often they do not produce any visible light.

The research is published in the journal Monthly Notices of the Royal Astronomical Society.