21 January 2013 Last updated at 01:00 ETBy Rebecca Morelle Science reporter, BBC World Service
Gamma-ray bursts can occur when two neutron stars merge
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A gamma ray burst, the most powerful explosion known in the Universe, may have hit the Earth in the 8th Century.
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.