The phenomenon in 774 A.D. may have been a previously unrecognized supernova explosion and could explain a mysterious spike in carbon-14 levels in that year's growth rings in Japanese cedar trees, Nature reported Wednesday.
Jonathon Allen, a biochemistry major at the University of California, Santa Cruz, heard about research in Japan that found an odd spike in carbon-14 levels in tree rings, probably caused by a burst of high-energy radiation striking the upper atmosphere and increasing the rate at which carbon-14 is formed.
However, the only known causes of such bursts are supernova explosions or gigantic solar flares, and there was no historical record of any such events in the dates indicated by the tree rings.
Allen, intrigued, went on the Internet. "I just did a quick Google search," he said.
"I knew that going that far back, there's very limited written history," he said. "The only things I'd ever seen or heard of were religious texts and 'chronicles' that listed kings and queens, wars and things of that nature."
His Internet search led to eighth-century entries in the Anglo-Saxon Chronicle in an online library of historical and legal documents hosted by Yale University, where he found a reference to a "red crucifix" that appeared in the heavens "after sunset."
"It made me think it's some sort of stellar event," Allen said.
Astronomers say they are impressed by Allen's find.
"The wording suggests that the object was seen in the western skies shortly after sunset," Geza Gyuk, an astronomer at Chicago's Adler Planetarium, said. "That would mean that it would have moved behind the Sun [where it could not be seen] as Earth orbited the Sun. That, along with the dimness of the 'new star' due to dust would go a long way to explaining why no one else would have seen or recorded the event."
Numbers of supernovae now known to astronomers "are simply missing" in the historical record, Gyuk said. "The sky is a large place and the historical record is not very good."