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Researchers discover proof of massive gamma-ray burst striking Earth in 8th century

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Image of entire sky in 100 MeV or greater gamma rays as seen by the EGRET instrument aboard the CGRO spacecraft.

Astronomers Valeri Hambaryan and Ralph Neuhӓuser have discovered proof that a massive short duration gamma-ray burst hit the earth in the 8th century. The intense blast of high-energy radiation could have caused a mass-extinction event if it had been just a tad bit closer to the earth. Scientists estimate that the event emanated from 3,000 to 12,000 light years away from the Sun, just far enough for Earth’s natural defenses to shield inhabitants from total destruction.

Researchers reached their conclusion after discovering high levels of the isotope 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. Carbon-14 and Beryllium-10 form when radiation from space collides with nitrogen atoms, which then decay to these heavier forms of carbon and beryllium. Earlier research ruled out the explosion of a nearby massive star (a supernova) as nothing was recorded in observations at the time and no remnant has ever been found. In addition, a massive solar flare has also been ruled out because they are not powerful enough to cause the levels of Carbon-14 found in the tree rings. As further evidence, they noted that the spectacular, vivid displays of northern and southern lights were not reported in historical records of that time period either.  The cause of the event remains a mystery.

The researchers explained how earth inhabitants dodged a bullet:

“If the gamma ray burst had been much closer to the Earth it would have caused significant harm to the biosphere. But even thousands of light years away, a similar event today could cause havoc with the sensitive electronic systems that advanced societies have come to depend on. The challenge now is to establish how rare such Carbon-14 spikes are i.e. how often such radiation bursts hit the Earth. In the last 3000 years, the maximum age of trees alive today, only one such event appears to have taken place.”

Sources: Monthly notices of the Royal Astronomical Society