Astronomy
Image still from animation showing a hypernova burst

New Study Suggests Earth Hit by Gamma Ray Blast 1200 Years Ago



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Image still from animation showing a hypernova burst
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"New Study Suggests Earth Hit by Gamma Ray Blast 1200 Years Ago"
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Image by: NASA
© This file is in the public domain because it was solely created by NASA http://www.nasa.gov/images/content/125499main_HyperNova_sm.jpg

Life on Earth, while robust, is also fragile. The biosphere can only support higher lifeforms within a very narrow range. Mass extinction events have occurred numerous times in Earth's past and no doubt will happen many more times in the future.

Various cataclysmic events happen that place all or most life at high risk. Among the planet-threatening events that have destroyed much of the life on Earth are: massive super volcanoes erupting, gigatons of methane gas changing the atmosphere and robbing animals of life-giving oxygen, gigantic space rocks—asteroids and comets miles wide—slamming into the planet and plunging the world into darkness…

But perhaps the worst wild card of all are the killer gamma rays that could burn through the protective atmosphere of Earth and scour the surface of the planet destroying virtually all life above ground. Supermassive stars exploding into supernovas or hypernovas can create such a wave of killer radiation that will travel at light speed. If a relatively nearby star goes supernova, the cosmic gamma radiation created could reach the Earth with enough intensity to wipe out the human race.

What are cosmic rays?

Cosmic rays are highly charged particles of matter that cross interstellar space. Most cosmic rays don't radiate outward in a straight direction because they are warped by gravity and magnetic fields when traveling distances measured in light years.

A particular type of cosmic ray, however, known as the gamma ray, is unaffected by fields and can cross huge distances of interstellar space. Its course is not warped because gamma rays have similar properties to light.

Gamma ray bursts are created by titanic events: the collision of black holes, neutron stars or a hypernova. The energy released by such events is known to be the most powerful and dangerously destructive in the universe.

It's believed at least one mass extinction occurring in Earth's distant past was triggered by a bombardment of gamma rays.

While that event was many hundreds of millions of years ago, evidence emerged during 2012 that Earth was hit by a blast of radiation—a blast much weaker than the one thought to have caused a great extinction. This radiation hit Earth during the Middle Ages and its origin puzzled researchers.

New study suggests gamma ray burst

A cosmic explosion created by the massive collision of neutron stars or two black holes sent a shock wave of charged particles racing toward Earth. That's the conclusion of new research by a team of scientists studying the clues left behind by the event.

Trees are often used by scientists as natural time capsules. They draw from the existing environment and incorporate parts of the soil and atmosphere within their cells that are locked away in the vault of time.

The discovery that Earth was hit by cosmic radiation—probably a gamma ray burst (GRB)—came to light when studies were done of old Japanese trees. The trees lived about 1,200 years ago and contained unusually high levels of carbon-14, an isotope that would be created when living matter is exposed to gamma rays.

Another team found support of the Japanese discovery thousands of miles away in the South Pole ice. That team found the isotope beryllium-10 encapsulated in pristine ice core samples at a depth calculated to be from the late Eighth Century.

Back in 2012, a research team proposed that a massive solar flare might have caused the residue from the blast. But many rejected the hypothesis because solar radiation is believed too weak to create the amount of beryllium-10 found in the ice and carbon-14 discovered in the ancient Japanese cypress trees.

German team finds evidence of gamma ray burst

Professor Ralph Neuhauser of the Institute of Astrophysics at the University of Jena, Germany, is a co-author of the new study, "A Galactic short gamma-ray burst as cause for the 14C peak in AD 774/5," that proposes a huge explosion happened in the galaxy within the celestial neighborhood of Earth.

The Earth and humanity were very lucky. If the event had been measurably closer, humans may have died off in about 780 A.D.

Instead, the researchers note, "We estimate the distance towards this short GRB to be ∼1–4 kpc—sufficiently far away, so that no extinction event on Earth was triggered. This is the first evidence for a short GRB in our Galaxy. "

Neuhauser, writes the BBC, explains that "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. 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."

How distant was the explosion? "Our conclusion was it was 3,000 to 12,000 light-years away—and this is within our galaxy," Neuhauser said.

Although a significant number of scientists do not believe a big solar flare can account for the isotopes, some are skeptical about the GRB hypothesis.

Adrian Melott, from the University of Kansas, is quoted by the BBC as observing that, "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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