Astronomers have allayed fears of doomsday 2012 supernova explosion, saying that given the vastness of the universe the long times between supernovae, there is no threatening star close enough to hurt the Earth.

According to Francis Reddy of NASA's Goddard Space Flight Center, the X- and gamma-ray radiation from a supernova could damage the ozone layer so that any planet with life on it near a star that goes supernova can have problems. With less ozone, more UV lights reach the Earth's surface and this could be lethal to some organism, including phytoplankton.

Astronomers estimate that about one or two supernovae explode each century in the Milky Way but these are very far away, adding that the blast must occur less than 50 light years away for it to experience the Earth's ozone layer.

NASA also explained another explosive event, called a gamma-ray burst which happens when a massive star collapses on itself, or when two compact neutron stars collide, which results to 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," the NASA report said.

Astronomers said a gamma-ray burst could affect Earth the same way as a supernova although at a much greater distance, estimated at 10,000 light-years away with each separated by about 15 million years, on average. The 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," Reddy's report said.