Space Explosion To Blame For Tree Ring Mystery, Astronomers Say
YAHOO.COM - More than 1,200 years ago, some mysterious event was recorded in tree rings in a Japanese cedar forest.
While one study suggested a solar flare was to blame, a new group of researchers are pointing toward a gamma-ray burst, a powerful space explosion.
The ancient cedar trees record a rare event around 774 or 775 A.D. This
shows up in a sharp rise in the amount of radioactive carbon-14 and
beryllium-10 recorded in the trees' rings, which can be created by
incoming particles from space.
But what caused an influx of radiation?
Tree ring mystery
According to astronomers Valeri Hambaryan and Ralph Neuhauser of the
Astrophysics Institute of the University of Jena in Germany, the most
likely culprit was a gamma-ray burst. [Amazing Solar Flare of Oct. 22, 2012 (Photos)]
These bursts can be caused when two compact objects, such black holes
or neutron stars, slam into each other and release a flood of
high-energy gamma-ray radiation.
Such an interpretation, the scientists argue, fits the tree ring
mystery, because a gamma-ray burst would be powerful enough to cause the
uptick in carbon-14
and beryllium-10. It also fits with the fact that no rare celestial
event was observed that year on Earth, at least according to records
The researchers calculated that a gamma-ray burst at a distance of 3,000 and 12,000 light-years from Earth best fits the data.
"If the gamma-ray burst had been much closer to the Earth it would have
caused significant harm to the biosphere," Neuhauser said in a
statement. "But even thousands of light-years away, a similar event
today could cause havoc with the sensitive electronic systems that
advanced societies have come to depend on."
The rare forms of carbon and beryllium, which are heavier than the
normal varieties of those elements, are created when radiation from
space collides with nitrogen atoms in Earth's atmosphere, which then
decay into carbon-14 and beryllium-10.
Both chemicals are unstable and decay on predictable time scales,
allowing scientists to trace these particular tree rings back to such a
specific time in the past. The fact that the jump in carbon-14 and
beryllium-10 was only seen in one year's rings means whatever sparked
their creation was short-lived.
"The challenge now is to establish how rare such carbon-14 spikes are,
i.e., how often such radiation bursts hit the Earth," Neuhauser said.
"In the last 3,000 years, the maximum age of trees alive today, only one
such event appears to have taken place."
The researchers say a gamma-ray burst explanation fits better than a
solar flare, because most flares from the sun would not be powerful
enough to create such a spike. Plus, they argue, a super-strong solar
flare would likely have created extra-special aurora displays, which
were not seen, according to historical records.
However, astrophysicists Adrian Melott of the University of Kansas and
Brian Thomas of Washburn University say a flare would have to have been
only about 10 or 20 times more powerful than the greatest flare on
record, the so-called Carrington event of 1859. Since the records don't go back very far, such an occurrence is not out of the realm of possibility, they say.
To distinguish between the different interpretations, historians will
have to look for further hints in the historical records. Neuhauser and
Hambaryan also suggest looking for the object that might have resulted
from the merger that caused the gamma-ray burst, which would be a
1,200-year-old black hole or neutron star that lies between 3,000 to
12,000 light-years away, but lacks the characteristic gas and dust
clouds of a supernova remnant.
They report their findings Jan. 21 in the journal Monthly Notices of the Royal Astronomical Society.
Tuesday, June 18 2013 7:25 PM EDT2013-06-18 23:25:07 GMT
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