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Wolf-S
2012-Jun-09, 10:39 PM
1,200-Year-Old Cosmic Blast Captured in Japanese Trees

A surplus of radioactive atoms in Japanese trees may point to an unrecorded astronomical event that showered Earth with cosmic rays about 1,200 years ago.

http://news.nationalgeographic.com/news/2012/06/120607-cosmic-rays-supernovae-japan-trees-mystery-space-science/

This link also has a historical reference to a quote by a chronicler 776 AD about "fiery and fearful signs in the heavens":

Vast cosmic event leaves record in ancient trees
http://www.newscientist.com/article/dn21878-vast-cosmic-event-leaves-record-in-ancient-trees.html
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So it's 20 times more radiation than normal... I'm wondering how large a supernova could produce this. And no observations of the actual event? I'm thinking that maybe the possible supernova was visible only from Southern hemisphere so that would explain the lack of historical records of a new star? Or would the Earth act in this case as a radiation shield for Northern hemisphere?

antoniseb
2012-Jun-09, 11:23 PM
I haven't seen anything about trees from elsewhere, but if no one looked yet, there might be something more specific in a few months or years.

Or would the Earth act in this case as a radiation shield for Northern hemisphere?
From Cosmic Rays, it doesn't matter. They do their work in the upper atmosphere, and create the Carbon-14 and Beryllium-10 up there.

Squink
2012-Jun-10, 08:24 PM
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 C-14 record.http://www.scientificamerican.com/article.cfm?id=mysterious-radiation-burst-rec

New Scientist adds (http://www.newscientist.com/article/dn21878-vast-cosmic-event-leaves-record-in-ancient-trees.html?DCMP=OTC-rss&nsref=online-news) a potentilly woo inspiring note:
Mike Baillie, a tree ring researcher at Queen's, has found evidence in the historical record that suggests something unusual did indeed happen at that time. The 13th-century English chronicler Roger of Wendover is quoted as saying: "In the Year of our Lord 776, fiery and fearful signs were seen in the heavens after sunset; and serpents appeared in Sussex, as if they were sprung out of the ground, to the astonishment of all."

Ara Pacis
2012-Jun-11, 12:27 AM
That first article suggested that a superflare might be the cause. I clicked a link (http://news.nationalgeographic.com/news/2012/05/120516-superflares-sun-stars-planets-hot-jupiters-nasa-space-science/) there and apparently researchers now suspect that superflares tend to happen on sun-like stars with terrestrial planets by connecting to their magnetic field. While, Mercury is deemed to be too small, I wonder if Venus might be close enough if it had a strong magnetic field at one point in time when the sun was hotter. If a sun-Venus connection were possible, would that and related superflares explain some questions we have about the geophysical characteristics of Venus and the evolution of life on earth? Or does that sounds like EU nonsense?

flynjack1
2012-Jun-11, 03:24 AM
What about a GRB? Potentially far enough not to completely wipe out life?

antoniseb
2012-Jun-11, 01:55 PM
What about a GRB? Potentially far enough not to completely wipe out life?
I've been thinking about that... I think the problem is that a Supernova has a year or so to deliver all the cosmic rays, and a GRB has a few seconds... so unless the GRB were in the LMC, I'm not sure it could do the job.

The calculation I haven't done is to estimate the excess number of C14 nuclei created that year, and then figure out how much energy had to be delivered to our upper atmosphere in the many-GeV range by this event. That could constrain the sources a bit.

publiusr
2012-Jun-11, 10:02 PM
That wasn't that long after Krakatau's (Kapi's) big eruption around 535 A.D. that David keys wrote about in Catastrophe. A one two punch?

Romanus
2012-Jun-12, 12:58 AM
I think a magnetar outburst is more likely; they are rare, extremely energetic, and (AFAIK) concentrated along the galactic plane, of which the Southern Hemisphere gets the best view (well, at least of the densest regions of the NH's "summer" Milky Way). A solar flare is most likely of all, though, as it also squares with reports of what might have been aurorae.

Bynaus
2012-Jun-12, 03:50 PM
@Ara Pacis: Venus has only a very weak field, and planetary magnetic fields are not expected to fluctuate on such short-term (~1300 years) timescales. Plus, if Mercury is too far away, Venus is as well. I think one crucial part of the model is that a Hot Jupiter will orbit its star faster than the latter rotates, therefore "winding up" the magnetic field lines until they snap. Since both Mercury and Venus orbit far beyond the co-rotation distance, the model would never work for them.

I would even assume that the occurence of short-period planets counter-indicates the presence of life (or at least observers) in the system, explaining why the inner solar system is suspiciously devoid of short-period planets, compared to the vast majority of the Kepler systems. In other words, we don't have them because we would not be here if there were short-period planets (causing superflares).

I think the most probable explanation of the 775 AD-event is a very strong solar flare / storm (much stronger than the 1857 event). The repetition of such an event might well cripple civilization, but that would have to be looked at in more detail.

Ara Pacis
2012-Jun-12, 09:43 PM
Right, I didn't think that a superflare was responsible, I was thinking of a time well before 775. I just happened to go off on a tangent. I actually posted about this in Q&A, with more detailed questions/conjectures.