Has a Biochem Undergrad Solved a Cosmic Radiation Mystery?

scibri writes "A few weeks ago, reports of a mysterious spike in carbon-14 levels in Japanese tree rings corresponding to the year 775 intrigued astronomers. Such a spike could only have been caused by a massive supernova or solar flare, but there was no evidence of either of these at that time. Until Jonathon Allen, a biochem undergrad at UC Santa Cruz, Googled it. He found a reference in the Anglo-Saxon Chronicle to a 'red crucifix' appearing in the sky in 774, and speculates that it could have been a supernova hidden behind a cloud of dust, which could mask the remnants of the exploded star from astronomers today."

No, he did not

[mapkinase]

He proposed an explanation more plausible than people before.

Could not have been...

[camperdave]

This could not have been caused by a supernova. A supernova would have affected almost the entire planet, not just Japan.

physics question

[slashmydots]

I didn't get way into physics in high school but I was interested. Hearing this explanation confuses me so there are probably more people than me who are wondering this. How exactly can cosmics radiation can cause carbon atoms in the atmosphere to gain neutrons? No new carbon is being formed, obviously, so existing carbon atoms would have to be turning into carbon-14 and I didn't think it was possible to just slip in another neutrons without basically blowing up the nucleus of any atom. I mean we don't "make" tritium for example by stuffing in more nuetrons magically, we have to sort it out of seawater. I would bet I could randomly throw my mouse and hit 3 physicists here at slashdot so could someone explain what the correlation between supernovas and carbon 14 is?

Re:Religious misinterpret phenomenon

[Baloroth]

And yet, without the religious text, there wouldn't even be a written record of what happened at all. I'd say everyone wins.

Re:physics question

[Anonymous Coward]

If your source of all things certain is wikipeding, you shouldn't bother posting replies.

Re:A few weeks ago in slashdot...

[Sir_Sri]

When you're talking about events 1200 years ago you're not exactly looking for a telescope picture.

There's evidence of a supernova, or possibly something else, from that time period in Japan. So what was it? Well, apparently in the UK they observed some weird shit that could have been a supernova. So it might actually have been a supernova.

Imagine if this was the other way. There was some written european evidence of some weird red thing in the sky in 774. What would tell what that red thing was? a spike in carbon 14 in tree rings from that time period would make 'supernova' a good guess.

It's not really a sciences problem, it's a language problem. Outside of Japan I bet most people didn't really care, and the Japanese didn't have the desire to search through piles of old foreign language documents on the vague guess they might say something that could have caused a carbon 14 spike in 773, 774 or 775. Digitized images and electronic search make that problem easier, and now the question for verification becomes one of finding if there are similar descriptions in other languages for that time period.

Re:Could not have been...

[camperdave]

Can't tell if stupid, or ignorant.

Well, for it to have affected the entire planet, the supernova would have had to be on the celestial equator. If it was displaced significantly from the celestial equator, then the radiant energy from the supernova simply wouldn't hit the Earth's surface at certain latitudes - for the same reasons that the polar regions experience periods of perpetual darkness.

Re:Could not have been...

[Anonymous Coward]

It's irrelevant because C14 is derived from N14 in the upper atmosphere, and the atmosphere is well-stirred. The higher C14 would get mixed in globally no matter which side of the Earth was irradiated.

The real issue is that all these sorts of "global event in year X" events start with a discovery at one or a few sites. For example, the iridium spike at the Cretaceous/Tertiary boundary was first found at Gubbio, Italy. Then it was found at dozens of other sites world-wide at the same boundary, but it took time to do those studies. Anyway, the original paper predicts that if you look elsewhere you should see similar spikes in C14 at that point in time in the record, which I assume people are already actively investigating. Give it a year or two and the possibility will either be confirmed (it is global) or negated (not found elsewhere, which probably means some other explanation).

It Seems Dubious on Physical Grounds

[careysub]

I looked into the literature on supernovas and carbon-14 and found this: http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19690024196_1969024196.pdf [nasa.gov] also see: http://journals.ametsoc.org/doi/abs/10.1175/1520-0469(1964)021%3C0134%3APOCBSP%3E2.0.CO%3B2 [ametsoc.org]

The 775 C-14 spike is 20 times the normal level. According to this paper the closest recent supernova (the Crab Nebula supernova in 1054) was only capable of producing a spike 8% more than normal.

To get a 2000% increase over normal you need a supernova 16 times closer, about 400 light years away, and 250 times brighter than 1054. The angular diameter of such a remnant today would be larger than the full moon, it seems unlikely that there are any dense dust clouds of this visible size for an object like this to hide behind. An obscure reference in the Anglo Saxon Chronicle does no a credible supernova make.