Unstable star threatens Earth - astronomer

Its name is WR104, and it could spell the end of the world.

A Sydney University astronomer has warned this week that the Earth could be destroyed when an unstable neighbouring star explodes.

Dr Peter Tuthill said that observing WR104, a star system in the Sagittarius constellation, made him feel like he was "looking down a rifle barrel".

When one of the system's central stars explodes as a supernova, it could send a narrow beam of gamma rays towards Earth. Some scientists believe gamma-ray storms have led to planet-wide mass extinctions.

WR104 is a spiral system 8000 light years from Earth. One of the two stars locked in binary at its centre is a Wolf-Rayet (imminent supernova) type star.

Tuthill has discovered that the pole the spiral spins on points almost exactly at Earth.

It recently has been discovered that gamma rays are fired out along a star system's polar axis.

Tuthill said the star was a "ticking bomb". "It's worrying enough. We do live on a fragile planet and this is one of the things that could be harmful. I used to appreciate this spiral just for its beautiful form, but now I can't help a twinge of feeling that it is uncannily like looking down a rifle barrel."

Though there was debate among scientists about the effect of gamma-radiation blasts, some predicted they could burn off 50 per cent of the ozone layer, creating "dramatic" climate events like rampant global warming or even a nuclear winter, he said.

Despite the threat posed by the star, Tuthill said he was not "selling up the real estate and moving to the Moon just yet". There were plenty of uncertainties that could mean the beam missed Earth and it may not happen for thousands of years yet.

However, Canterbury University astronomer Associate Professor Peter Cottrell said the death star theory was "nice speculation", but "I wouldn't get too worried".

Cottrell said Earth was "pretty small" and could easily be missed by the radiation.

"Crossing the road is probably more of a danger."