17 December 2011

NASA Debunks End of World by Supernova Scenario

Death by Supernova is off the list of end of the world scenarios.

A doomsday prediction that a supernova explosion in 2012 will cause the end of the world is false. Astronomers at NASA's Goddard Space Flight Center say that there is no threatening star close enough to hurt Earth

A supernova is an exploding star that expends more energy than normal. Supernovae or supernovas are extremely luminous and emit a powerful burst of radiation that often briefly outshines an entire galaxy. During this period a supernova can radiate as much energy as the Sun is expected to emit over its entire life span. The explosion expels much or all of a star's material at a velocity of up to 30,000 km/s (10% of the speed of light), driving a shock wave into the surrounding interstellar medium. This shock wave sweeps up an expanding shell of gas and dust called a supernova remnant.

It is estimated that one to two supernovae explode in the Milky Way each century. For the Earth's ozone layer to experience damage, the supernova should occur less than 50 light years away. All of the nearby stars capable of going supernova are much farther than this.

The closest star to the Earth is the Sun. And it is nowhere near to becoming a supernova. In terms of disruption the Earth encounters from the Sun is a coronal mass ejection. It is an explosion of the Sun's atmosphere that propagates into space in the form of a cloud. It can disrupt satellites, cell phones and cause electricity disruptions. To an extent, this is the worst we have experienced with the Sun

Video: The Crab Nebula is a remnant of a Supernova seen in the year 1054

Any planet near a supernova will surely be affected. If it was the Earth, X- and gamma-ray radiation from the supernova could damage the ozone layer, which protects us from harmful ultraviolet light in the sun's rays. The less ozone there is, the more UV light reaches the surface. At some wavelengths, just a 10 percent increase in ground-level UV can be lethal to some organisms, including phytoplankton near the ocean surface. Because these organisms form the basis of oxygen production on Earth and the marine food chain, any significant disruption to them could cascade into a planet-wide problem.

Another explosive event, called a gamma-ray burst (GRB), is often associated with supernovae. When a massive star collapses on itself -- or, less frequently, when two compact neutron stars collide -- the result is the birth of a black hole. As matter falls toward a nascent black hole, some of it becomes accelerated into a particle jet so powerful that it can drill its way completely through the star before the star's outermost layers even have begun to collapse. If one of the jets happens to be directed toward Earth, orbiting satellites detect a burst of highly energetic gamma rays somewhere in the sky. These bursts occur almost daily and are so powerful that they can be seen across billions of light-years.

Video: Anatomy of a Solar Explosion

A gamma-ray burst could affect Earth in much the same way as a supernova -- and at much greater distance -- but only if its jet is directly pointed our way. Astronomers estimate that a gamma-ray burst could affect Earth from up to 10,000 light-years away with each separated by about 15 million years, on average. So far, the closest burst on record, known as GRB 031203, was 1.3 billion light-years away.

As with impacts, our planet likely has already experienced such events over its long history, but there's no reason to expect a gamma-ray burst in our galaxy to occur in the near future, much less in December 2012.

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