NASA-International Space Station

The star, called T Pyxidis, is set to self-destruct in an explosion called a supernova with the force of 20 billion megatons of TNT.

Although the star is thought to be around 3,260 light-years away, a fairly short distance in galactic terms – the bang from the thermonuclear explosion could strip away the Earth's ozone layer, the scientists said.

Astronomers from Villanova University, Philadelphia, in the US, said the International Ultraviolet Explorer satellite has revealed them that T Pyxidis is really two stars, one called a white dwarf that is sucking in gas and progressively growing. When it reaches a decisive mass it will blow itself to pieces.

It will become as intense as all the other stars in the galaxy put together, they said. The Hubble space telescope has photographed the star preparing for its big bang with a series of minor blasts or "burps", called novas.

These explosions came frequently about every 20 years from 1890 – but stopped after 1967. So the next blast is nearly 20 years late, said scientists Edward M Sion, Patrick Godon and Timothy McClain at the American Astronomical Society in Washington

Robin Scagell, vice-president of the UK's Society for Popular Astronomy, said: "The star may definitely became a supernova soon – but soon could still be a long way off so don't have nightmares."

Astronomers have revealed a new kind of cosmic explosion that seems to have originated from an extremely massive star one that's over 200 times the size of our own sun.

Scientists first discovered SN2007bi, the supernova in question, in 2007, and were instantly puzzled. It finally faded just recently. "It was much brighter, and it was bright for an extremely long time," said researcher Paolo Mazzali, of the Max-Planck Institute for Astrophysics in Germany, in the report. "We could watch this thing almost two years after it was discovered, where you normally don't see anything anymore."

The resultant explosion was about 50 to 100 times brighter than a distinctive supernova and rewrites what astronomers knew about star formation. 2N2007bi has turned out to be a pair-instability supernova, which releases protons so vigorous that they generate pairs of electrons and their anti-matter opposites, positrons, the report said. The two meet, eradicate each other, and cause the star itself to collapse, "igniting its oxygen core in a runaway nuclear explosion that eats up the whole star."