'Cosmic bang' hit Medieval Earth

In 2012 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 a study suggests it was the result of two black holes or neutron stars merging in our galaxy.

This collision would have hurled out vast amounts of energy.

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

Last year, a team of researchers found that some ancient cedar trees in Japan had an unusual level of a radioactive type of carbon known as carbon-14.

n 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.

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