'Powerful' gamma ray burst may have 'hit Earth in 8th Century'
A new study has suggested that a gamma ray burst, the most powerful explosion known in the Universe, may have hit the Earth in the 8th Century.
Last year, a team of researchers found evidence that our planet had been struck by a blast of radiation during the Middle Ages, but there was debate over what kind of cosmic event could have caused this.
Now the latest study, published in the journal Monthly Notices of the Royal Astronomical Society, suggested that it was the result of two black holes or neutron stars merging in our galaxy.
Researchers suggest this collision would have hurled out vast amounts of energy, according to the BBC.
In 2012, a research team found that some ancient cedar trees in Japan had an unusual level of a radioactive type of carbon known as carbon-14.
In Antarctica, too, there was a spike in levels of a form of beryllium - beryllium-10 - in the ice.
These isotopes are created when intense radiation hits the atoms in the upper atmosphere, suggesting that a blast of energy had once hit our planet from space.
Using tree rings and ice-core data, researchers were able to pinpoint that this would have occurred between the years AD 774 and AD 775, but the cause of the event was a puzzle.
The possibility of a supernova - an exploding star - was put forward, but then ruled out because the debris from such an event would still be visible in telescopes today.
Another team of US physicists recently published a paper suggesting that an unusually large solar flare from the Sun could have caused the pulse of energy. However some others in the scientific community disagree because they do not think that the energy produced would tally with the levels of carbon-14 and beryllium-10 found.
Now German researchers put forward another explanation: a massive explosion that took place within the Milky Way.
Professor Ralph Neuhauser from the Institute of Astrophysics at the University of Jena is one of the authors of the paper.
He said that they 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 they observed - and found that is fully consistent.
These enormous emissions of energy occur when black holes, neutron stars or white dwarfs collide - the galactic mergers take just seconds, but they send out a vast wave of radiation.
Gamma-ray bursts are very, very explosive and energetic events that occurred 3,000 to 12,000 light-years away - but within our galaxy, said Prof Neuhauser.
Although the event sounds dramatic, our medieval ancestors might not have noticed much, the researchers noted.
Observations of deep space suggest that gamma ray-bursts are rare. They are thought to happen at the most every 10,000 years per galaxy, and at the least every million years per galaxy.
Prof Neuhauser said it was unlikely Planet Earth would see another one soon, but if we did, this time it could make more of an impact.