Supernova star too close for comfort

Astronomers have identified a ticking time-bomb in space that lies perilously close to the Earth, they revealed today. The star, called T Pyxidis, looks set to explode as a supernova with the force of 20 billion billion billion megatons of TNT.

But it lies less than 3,260 light-years away in our own galaxy – close enough in cosmic terms for a blast to have a possibly devastating impact on our planet.

In their news release, the scientists say that a thermonuclear explosion at such a close distance will “fry the Earth”, dumping as much gamma ray energy as 1,000 solar flares at once. It will strip away the ozone layer, allowing deadly radiation to bombard all life.

The star, in the southern constellation of Pyxis, the compass, has erupted before in cosmic burps as a normal, less powerful nova. Explosions were seen at approximately 20-year intervals in 1890, 1902, 1920, 1944 and 1967. But it is 44 years overdue for its next blast and astronomers do not know why.

New studies using the International Ultraviolet Explorer satellite show that it is much closer to us than previously thought and is a double-star system with one star like the sun and a smaller denser star called a white dwarf.

The white dwarf is steadily becoming more massive as gas flows onto it from its companion. The scene looks set for it to reach a critical stage – called the Chandrasekhar Limit – where it suddenly collapses under its own weight triggering an unimaginably powerful thermonuclear explosion that destroys it completely. The star will then become as bright as all other stars in the galaxy put together and shine like a beacon halfway across the universe.

This catastrophic event, called a Type Ia supernova, will release ten million times more energy than a normal nova.  The doomsday scenario was described today by astronomers Edward M. Sion, Patrick Godon and Timothy McClain from Villanova University, Philadelphia, at a conference of the American Astronomical Society in Washington.

They said that pictures taken by the Hubble space telescope of shells of material thrown off in previous eruptions fitted the view that star is set to go supernova.

It sounds scary stuff. And the astronomers’ news release suggest it will happen “soon”. But I contacted the lead researcher, Dr Ed Sion, and he told me: “At the accretion rate we derived, the white dwarf in T Pyxidis will reach the Chandrasekhar Limit in ten million years. I hope this alleviates any worry by readers.”

So no need to lose any sleep!

Picture: A Hubble photo of T Pyxidis, showing the shell of debris thrown off by a nova blast. (NASA/ESA).

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By Paul Sutherland

Paul Sutherland has been a professional journalist for nearly 40 years. He writes regularly for science magazines including BBC Sky at Night magazine, BBC Focus, Astronomy Now and Popular Astronomy, plus he has authored three books on astronomy and contributed to others.

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