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.Perhaps the Vogons were trying to put an interstellar bypass in our neighborhood at the time.
The only known events that can produce a 14C spike are floods of γ-rays from supernova explosions or proton storms from giant solar flares. But neither seems likely, Miyake says, because each should have been large enough to have had other effects that would have been observed at the time.
"It would be fascinating," Baker adds, "if there were some record in China or in the Middle East that reported powerful aurora or some other such event" around the same time as the observed 14C increase.
07 June 2012
Unknown "massive cosmic event" in AD 774
In a study published in the current issue of Nature, Japanese scientists studying dendrochronology report that the Earth experienced an unexplained intense burst of high-enegy radiation in AD 774 or 775.