Why don’t we know what blew up in 774?

Nature asks a question that gets more peculiar the more one considers it. A Japanese researcher looking at tree rings from two ancient cedars found unmistakable traces of a giant burst of cosmic rays in 774 CE. Something big and dramatic left a layer of carbon 14 – something like an enormous solar flare or a supernova. But the thing is nobody back then seems to have noticed it:

The radiation burst, which seems to have hit between ad 774 and ad 775, was detected by looking at the amounts of the radioactive isotope carbon-14 in tree rings that formed during the ad 775 growing season in the Northern Hemisphere. The increase in 14C levels is so clear that the scientists, led by Fusa Miyake, a cosmic-ray physicist from Nagoya University in Japan, conclude that the atmospheric level of 14C must have jumped by 1.2% over the course of no longer than a year, about 20 times more than the normal rate of variation. Their study is published online in Nature today1.

“The work looks pretty solid,” says Daniel Baker, a space physicist at the University of Colorado’s Laboratory for Atmospheric and Space Physics in Boulder, Colorado. “Some very energetic event occurred in about ad 775.”

A massive supernova, for example, should have been bright enough to produce a ‘new’ star visible even in the daytime, as was the case for two known supernovae in ad 1006 and ad 1054. Such an explosion would have needed to be brighter than either of these, Miyake says, because those events were not large enough to leave traces in the 14C record.

It is possible, he says, that the proposed event might have occurred in the far southern skies, where astronomers of the era wouldn’t have seen it. But still, he says, if it did happen, today’s X-ray and radio astronomers should have found signs of a “tremendously bright” remnant of the explosion.

As for solar flares, he says, anything that could have produced the required amount of super-high-energy protons would have vastly exceeded the most intense solar outburst ever recorded. There should have been a historical record of extraordinary auroras — not to mention that such a gigantic flare would probably have destroyed the ozone layer, with devastating ecological consequences.

The fun part is checking out all the comments under the article – there are a lot of scientists (armchair and otherwise) starting to speculate about various miracles, lights in the sky, dragon sightings and other strange phenomena from 774 that could maybe… just maybe… have something to do with this.