Wolf-Rayet 104 Has Us Locked in its Gunsights -- Are We in Danger of an Extinction Level GRB?

08/16/2014 06:03PM

Wolf-Rayet 104 Has Us Locked in its Gunsights -- Are We in Danger of an Extinction Level GRB?
Forget about global warming and the climatic changes caused by man's exploitation of our natural resources. These events are child's play compared to what Wolf-Rayet 104 (WR 104) may have in store for us. WR 104 is now in the last known stable phase for a massive star of this type and is only about 8000 light years away. The problem is that its polar orientation appears to be "face-on" to Earth's line of sight. Essentially, we are staring right down a gun barrel. If WR 104 collapses into a Supernova (as expected) and releases a Gamma Ray Burst (GRB), our Solar System could be in the direct path of a highly collimated jet of destruction and such an event could end life as we know it.

But will it happen in the next thousand years or in the next 500,000 years? Nobody knows... And nobody can do anything about it because the GRB and optical photons from the Supernova would arrive here simultaneously. Our only hope is that a few degrees one way or the other in the orientation of WR 104 could make all the difference in the world.

This would not be the first time that a GRB caused an Extinction Level Event (ELE) here on Earth. Scientists at NASA and the University of Kansas say that a mass extinction on Earth hundreds of millions of years ago could have been triggered by a GRB, but the scientists do not have direct evidence that such a burst activated this ancient extinction. The strength of their work is in their atmospheric modeling -- essentially a "what if" scenario.

The scientists calculated that gamma ray radiation from a relatively nearby star explosion, hitting the Earth for only ten seconds, could deplete up to half of the atmosphere's protective Ozone layer. Recovery could of the Ozone layer would take at least five years. However, with the Ozone layer damaged, Ultraviolet (UV) radiation from the Sun could kill much of the life on land and near the surface of oceans and lakes. That in itself would constitute an Extinction Level Event. But the real long term killer would be the disruption of the food chain.

GRBs in our Milky Way galaxy are indeed rare, but scientists estimate that at least one nearby GRB likely hit the Earth in the past billion years.

"A Gamma Ray Burst originating within 6000 light years from Earth would have a devastating effect on life," according to Dr. Adrian Melott of the Department of Physics and Astronomy at the University of Kansas. "We don't know exactly when one came, but we're rather sure it did come and left its mark. What's most surprising is that just a 10 second burst can cause years of devastating Ozone damage."

GRBs are the most powerful explosions known. Most originate in distant galaxies and a large percentage likely arise from explosions of stars over 15 times more massive than our Sun. A burst creates two oppositely directed and highly collimated beams of gamma rays that race off into space.

Brian Thomas of University of Kansas says that a Gamma Ray Burst may have caused the Ordovician extinction 450 million years ago, killing 60 percent of all marine invertebrates. At that time, life was largely confined to the sea, although there is evidence of primitive land plants during this period. To put things in relative perspective, the Ordovician extinction was about 200 million years before the time of the dinosaurs. The first life on Earth is thought to have appeared about 3.5 billion years ago.

In their work, the team used detailed computer models to calculate the effects of a nearby Gamma Ray Burst on the atmosphere and the consequences for life.

Thomas, with Dr. Charles Jackman of NASA's Goddard Space Flight Center in Greenbelt, Maryland, calculated the effect of a nearby GRB on the Earth's atmosphere. Gamma rays, a high energy form of light, can break molecular Nitrogen (N2) into Nitrogen atoms, which react with molecular Oxygen (O2) to form Nitric Oxide (NO). NO will destroy Ozone (O3) and produce Nitrogen Dioxide (NO2). NO2 will then react with atomic Oxygen to reform NO. More NO means more Ozone destruction. Computer models show that up to half the Ozone layer is destroyed within weeks. Five years on, some of the Ozone reforms, but at least 10 percent remains destroyed.

Next Thomas and Daniel Hogan, also of the University of Kansas, calculated the effect of UV radiation on life. Deep sea creatures living several feet below water would be protected. Surface dwelling plankton and other life near the surface, however, would not survive. This would be a major problem, as Plankton is the foundation of the marine food chain.

Dr. Bruce Lieberman, a paleontologist at the University of Kansas, originated the idea that a Gamma Ray Burst specifically could have caused the great Ordovician extinction 200 million years before the dinosaurs. An ice age is thought to have caused this extinction. But a Gamma Ray Burst could have caused a fast die-out early on and also could have triggered the significant drop in surface temperature on Earth.

"One unknown variable is the rate of local Gamma Ray Bursts," said Thomas. "The bursts we detect today originated far away billions of years ago, before the Earth formed. Among the billions of stars in our Galaxy, there's a good chance that a massive one relatively nearby exploded and sent gamma rays our way."

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