Nice idea, but a full on solar flare is way more likely and may
produce similar effects. Just how do we tell the difference? What is
needed is someway to determine the effect of a solar flare in the
first instance so that we can determine frequency. In short we are
running blind.
In the meantime we have notable signal in the data stream that lacks
confirmation so far from alternative data. The explanation is
creditable but unprovable for now.
I continue to be impressed by just how successfully the Earth's
envelope protects life on Earth. If this explanation holds up and as
much holds up for solar flares, then we have nothing to worry about
from that quarter.
i do not think that the picture is convincing either.
Gamma-ray burst 'hit Earth in 8th
Century'
By Rebecca Morelle
21 January 2013
A gamma ray burst, the most powerful explosion known in the
Universe, may have hit the Earth in the 8th Century.
In 2012 researchers
found evidence that our planet had been struck by a blast of
radiation during the Middle Ages, but there was debate over what kind
of cosmic event could have caused this.
Now a study suggests
it was the result of two black holes or neutron stars merging in our
galaxy.
This collision would
have hurled out vast amounts of energy.
The research
is published in the journal Monthly Notices of the Royal
Astronomical Society.
Last year, a team
of researchers found that some ancient cedar trees in Japan had
an unusual level of a radioactive type of carbon known as carbon-14.
In Antarctica, too,
there was a spike in levels of a form of beryllium - beryllium-10 -
in the ice.
These isotopes are
created when intense radiation hits the atoms in the upper
atmosphere, suggesting that a blast of energy had once hit our planet
from space.
Using tree rings and
ice-core data, researchers were able to pinpoint that this would have
occurred between the years AD 774 and AD 775, but the cause of the
event was a puzzle.
The possibility of a supernova - an exploding star - was put
forward, but then ruled out because the debris from such an event
would still be visible in telescopes today.
Another team of US
physicists recently published a paper suggesting that an
unusually large solar flare from the Sun could have caused the pulse
of energy. However some others in the scientific community disagree
because they do not think that the energy produced would tally with
the levels of carbon-14 and beryllium-10 found.
So now German
researchers have offered up another explanation: a massive explosion
that took place within the Milky Way.
One of the authors of
the paper, Professor Ralph Neuhauser, from the Institute of
Astrophysics at the University of Jena, said: "We looked in the
spectra of short gamma-ray bursts to estimate whether this would be
consistent with the production rate of carbon-14 and beryllium-10
that we observed - and [we found] that is fully consistent."
These enormous
emissions of energy occur when black holes, neutron stars or white
dwarfs collide - the galactic mergers take just seconds, but they
send out a vast wave of radiation.
Prof Neuhauser said:
"Gamma-ray bursts are very, very explosive and energetic events,
and so we considered from the energy what would be the distance given
the energy observed.
"Our conclusion
was it was 3,000 to 12,000 light-years away - and this is within our
galaxy."
Although the event
sounds dramatic, our medieval ancestors might not have noticed much.
If the gamma-ray burst
happened at this distance, the radiation would have been absorbed by
our atmosphere, only leaving a trace in the isotopes that eventually
found their way into our trees and the ice. The researchers do not
think it even emitted any visible light.
Rare events
Observations of deep
space suggest that gamma ray-bursts are rare. They are thought to
happen at the most every 10,000 years per galaxy, and at the least
every million years per galaxy.
Prof Neuhauser said it was unlikely Planet Earth would see another
one soon, but if we did, this time it could make more of an impact.
If a cosmic explosion
happened at the same distance as the 8th Century event, it could
knock out our satellites. But if it occurred even closer - just a few
hundred light-years away - it would destroy our ozone layer, with
devastating effects for life on Earth.
However, this, said
Prof Neuhauser, was "extremely unlikely".
Commenting on the
research, Professor Adrian Melott from the University of Kansas, US,
said that although he thought a short gamma-ray burst was a
possible conclusion, his group's research suggested that a solar
flare was more likely based on observations of Sun-like stars in our
galaxy.
He said: "A
solar proton event and a short gamma-ray burst are both possible
explanations, but based on the rates that we know about in the
Universe, the gamma-ray burst explanation is about 10,000 times less
likely to be true in that time period."
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