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EXCLUSIVE: Gamma ray explosion irradiated Earth in eighth century

Recent evidence suggests that 1240 years ago the Earth was bombarded by a massive gamma-ray burst, the most powerful known explosion in the universe. Researchers studying ancient Japanese cedar trees have found unusually high levels of the isotope carbon-14, corresponding with a surge in beryllium-10 in Arctic ice at the same time, which suggest that a powerful flash of cosmic radiation hit our planet in AD 774 or 775. The carbon-14 concentrations discovered in the cedars is about 20 times levels normally expected to result from solar modulation.

The explosion was likely caused by the collision of two neutron stars, which released an apocalyptic two-second blast of radiation as their two massive cores fused into one. Fortunately, the event occurred thousands of light years away, so the impact on middle-age humans and other species was relatively minor.

“If the gamma-ray burst had been much closer to the Earth it would have caused significant harm to the biosphere,” said lead researcher, Dr. Ralph Neuhauser of the University of Jena in Germany. “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”.

If a similar burst occurred within 200 light-years or so of Earth, it would strip our ozone layer away on contact, and likely lead to the mass extinction of life on our planet. We can thank the stars that such occurrences are relatively rare, estimated to happen only a few times every million years.

In an exclusive interview with the Science Recorder, lead researcher  Dr. Ralph Neuhauser elaborated on the team’s recent discovery.

Science Recorder (SR): How did this finding come about in the first place?

Ralph Neuhauser (RN): Miyake et al. (June 2012, Nature) found a C-14 spike in tree rings dates AD 774/5, but could not find the cause. We considered a short gamma-ray burst and found that it is consistent with all observables from the C-14 spike.

SR: Your study mentions the cedar tree samples were supported by evidence of a surge in beryllium-10 in Antarctic ice at the same time. While trees have a limited life span, would it be possible to find clues about gamma-ray bursts before then in ice samples?

RN: Yes, ice samples are older, but also the Be-10 decays, as it is radio active. More such spikes in older ice can possibly be found.

SR: What potential effects could the burst have had on life on Earth?

RN: In AD 774/5, it did not have any effect and may not have been noticed at all by humans at that time. We are protected by the ozone layer against high-energy radiation. If we keep the ozone layer alive, we will also be protected in the future.

SR: What are your next steps with this study?

RN: We plan to search for a neutron star at the predicted distance and age range, which might have been produced in such a merger, which is seen as a gamma ray burst.

The group’s findings were announced Monday, January 19 in the Monthly Notices of Britain’s Royal Astronomical Society journal, and based on research conducted in 2012.

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