Source of ancient radiation traced back to exploding black holes - NEWS.com.au

Fallout: scientists say a pair of black holes may have collided in the 8th Century, bathing Earth in gamma radiation. Source: NASA

HERE'S another one to add to your apocalypse fears: Gamma radiation from exploding black holes.

And we've already been hit - in the Middle Ages.

Last year scientists found evidence that an enormous blast of radiation had ripped through the Earth's atmosphere in the 8th Century. But they did not know why - until now.

A supernova would be the obvious cause. But the remnants of such a huge nearby explosion would still be visible.

It's not there.

Now, a study points the finger at two intensely-dense neutron stars or black holes merging in a cataclysmic collision.

The event lasts a few seconds. The impact is galaxy-wide.

The study, published in Monthly Notices of the Royal Astronomical Society, examines the possible causes of unusual radioactive materials found in Japan and Antarctica.

In Japan, ancient cedar trees contained high levels of carbon-14.

In Antarctica, the radiation by-product beryllium-10 was found at a particular layer in the ice.

Both correlate with a very narrow date - AD 774 and AD775.

Professor Ralph Neuhauser from the University of Jena's Institute of Astrophysics said gamma radiation was the only suspect that fit all the modus operandi.

"We 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 we observed - and [it] is fully consistent," he said.

The only known causes for such enormous emissions of energy are when neutron stars, white dwarf - or even black holes - collide.

"Our conclusion was it was 3000 to 12,000 light-years away - and this is within our galaxy," Professor Neuhauser said.

Why was there no mass radiation poisoning of our 8th Century ancestors?

Because the explosion wasn't close enough. The gamma radiation was absorbed in our atmosphere, leaving behind isotopes that eventually fell to earth to be covered in ice or absorbed by trees.

Professor Neuhauser said the explosion probably wasn't even visible.

For it to rip away our ozone layer and ravage life on Earth's surface, the explosion would have to happen within a few hundred light years.

Don't expect another any time soon.

The collisions happen in our galaxy roughly once every 10,000 years.

The idea is not without its detractors. A United States research group says a solar flare is more likely to have been the source of the gamma radiation, even though one of the enormous scale necessary to produce that much radiation has never been seen.