Ancient celestial "red crucifix" might be missing supernova.
An eerie "red crucifix" seen in Britain's evening sky in ad 774 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. The link is suggested today in Nature by a US undergraduate student with a broad interdisciplinary background and a curious mind.
A few weeks ago, Jonathan Allen, a biochemistry major at the University of California, Santa Cruz, was listening to Nature's podcast when he heard about a team of researchers who'd found an odd spike in carbon-14 levels in Japanese tree rings. The spike probably came from a burst of high-energy radiation striking the upper atmosphere, increasing the rate at which carbon-14 is formed (see Mysterious radiation burst recorded in tree rings).
The was only one problem: the only known causes of such radiation are supernovas or gigantic solar flares, and the researchers knew of no such events in AD 774 or 775, the dates indicated by the tree rings.
Intrigued, Allen hit the internet. "I just did a quick Google search," he says.
Allen has a longstanding interest in history. "I knew that going that far back, there's very limited written history," he says. "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."
He found the Avalon Project, a digital library at Yale University, in New Haven, Connecticut. Scrolling to the year 774, he found the reference to a "red crucifix" that appeared in the heavens "after sunset".
"It made me think it's some sort of stellar event," he says. "And the next line had something referencing 'wonderful serpents' being seen in the land, which may or may not also have been a reference to things in the sky."
Furthermore, he noted, the new star's redness might indicate it was hidden behind a dust cloud dense enough to scatter all but red light -- a cloud that also masks the remnant of the supernova from modern astronomers' view.
Scientists in the field are impressed. Geza Gyuk, an astronomer at Chicago's Adler Planetarium, who has used the Anglo-Saxon Chronicle in the past, says Allen may be onto something. "The wording suggests that the object was seen in the western skies shortly after sunset," he says. "That would mean that it would have moved behind the Sun [where it could not be seen] as the 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."
Nevertheless, says Donald Olson, a physics professor with an interest in historical astronomy at Texas State University, San Marcos, "early chronicles can be difficult to interpret in an unambiguous way."
As far back as 1870, he says, John Jeremiah published an article in Nature that looked at exactly this description and proposed that it might have been an early description of the Northern Lights.
"Another possible explanation could be an ice-crystal display," adds Olson.
But, it could also have been a previously unrecognized supernova. Plenty of supernova now known to astronomers "are simply missing" in the historical record, says Gyuk. "The sky is a large place and the historical record is not very good."
Allen, J. Nature 486, 473 (2012).
Jeremiah, J. Nature 3, 174–175 (1870).
Related links in Nature Research
Mysterious radiation burst recorded in tree rings 2012-Jun-03
'Superflares' erupt on some Sun-like stars 2012-May-16
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Lovett, R. Mysterious radiation burst solved? [back by 2pm pls]. Nature (2012). https://doi.org/10.1038/nature.2012.10898