Earth was hit by gamma ray burst from space in eighth century, say
scientists
A massive cosmic explosion in deep space sent out a pulse of
high-energy radiation that hit the Earth between the years 774AD and
775AD when the emperor Charlemagne ruled much of Western Europe,
scientists have found.
The radiation pulse was probably the most intense cosmic event to
have affected the Earth in the past 3,000 years and it left an indelible
imprint in ancient cedar trees dating to that time, they said.
Last year, scientists discovered that tree rings from Japanese cedars
had much higher levels of radioactive carbon 14 than normal for the
years 774AD-775AD, suggesting that something dramatic must have happened
in the global atmosphere to trigger the rise of radioactive carbon.
One suggestion was an intense solar flare from the Sun, but this was
soon discounted as implausible.
Now Professor Ralph Neuhauser of the University of Jena in Germany
has suggested that the cosmic radiation came from a massive collision
either between two black holes or two massive stars located between
3,000 and 12,000 light years away, within our own Milky Way galaxy
Professor Neuhauser said that the cosmic collision caused a "gamma-ray
burst" - a flash on intense radiation and one of the most energetic
phenomena in the Universe.
Astronomers have seen them in other galaxies, but never in the Milky
Way.
"Over the past 3,000 years this was the most energetic event to have
hit the Earth," Professor Neuhasuer said. Even so, it is not likely to
have been noticed by anyone at the time because the burst lasted less
than two seconds, would not have left a visible impression in the sky
and was not close enough to cause species extinctions.
"If the gamma ray burst had been much closer to the Earth, it would
have caused significant harm to the biosphere. But even thousands of
light years away, a similar event today could cause havoc with the
sensitive electronics that advanced societies have come to depend on,"
Professor Neuhauser said. |