A new study shows the star, called T Pyxidis, is much closer than previously thought at 3,260 light-years away - a short hop in galactic terms.
It is set to self-destruct in an explosion called a supernova with the force of 20 billion billion billion megatons of TNT.
The blast from the thermonuclear explosion could strip away the Earth's ozone layer that keeps out deadly space radiation, scientists said.
The doomsday scenario was described today by astronomers from Villanova University in Philadelphia.
They said the International Ultraviolet Explorer satellite has shown them that T Pyxidis is really two stars, one called a white dwarf that is sucking in gas and steadily growing. When it reaches a critical mass it will blow itself to pieces.
It will become as bright as all the other stars in the galaxy put together and shine like a beacon halfway across the universe.
The experts said the Hubble space telescope photographed the star gearing up for its big bang with a series of smaller blasts or "burps", called novas.
These explosions came regularly about every 20 years from 1890, but stopped after 1967.
So the next blast is very overdue, 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 certainly became a supernova soon - but soon could still be a long way off so don't have nightmares."
