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Wednesday, 8 May, 2002, 14:10 GMT 15:10 UK
Cosmic catastrophe 'a certainty'
Eta Carinae will explode soon but luckily it is not pointing our way
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By Dr David Whitehouse
BBC News Online science editor
Sooner or later, a catastrophe from space will wipe out almost all life on Earth.

The few who might survive will wish they had died, they will struggle, forlornly, on a wrecked planet

Dr Arnon Dar
According to Dr Arnon Dar, of the Technion Space Research Institute, Israel, a particular type of exploding star going off anywhere in our region of the Universe would devastate our planet.

Using the latest statistics and calculations, he argues that a supermassive star collapsing at the end of its lifetime would form a black hole and send out a beam of destructive radiation and particles that would sterilise any planet in its path.

The odds are that any planet in our galaxy would be affected about once every one hundred million years. "It is a certainty; the timescales are comparable to mass extinctions seen in Earth's geological record," Dr Dar told BBC News Online.

No hiding place

Supermassive stars, those with a mass substantially greater than our Sun, are scattered throughout the galaxy. It is thought that when they collapse at the end of their lives, they eject an intense beam of radiation, called gamma-rays, into space.

Dr Arnon Dar
Dr Arnon Dar: Scientists are looking for the direct evidence
So powerful are these gamma-rays, and the energetic sub-atomic particles that follow in their wake, that they could have a major influence on life in our galaxy.

"If such a beam were to strike Earth, the effects would be totally devastating, unlike anything we could imagine," Dr Dar said.

On the side of Earth facing the explosion, searing shock waves will begin to rip through the atmosphere igniting infernos when they reach the ground.

Within moments of the arrival of the radiation from deep space, the atmospheric temperature will begin rising rapidly, wreaking havoc with global weather systems.

Destructive 'daughters'

All organic material on the surface of Earth will start to burn. Survivors will cower in caves and buildings. But the worst is yet to come.

The initial gamma-ray burst will last a fraction of a second. Almost immediately afterwards will come the cosmic rays, which will drench our planet for days. There will be no hiding place.

Cosmic rays are highly energetic particles travelling through space at almost the speed of light. They will slam into the atmosphere, depositing vast amounts of energy and creating swarms of destructive "daughter" particles.

These particles, called muons, will penetrate hundreds of metres into rocks so that few caves will offer protection and even deep-sea creatures will be affected by lethal doses of radiation.

The Earth's ecosystem will be destroyed. "The few who might survive will wish they had died," said Dr Dar. "They will struggle, forlornly, on a wrecked planet."

Dr Dar points out that many of the great extinctions that regularly punctuate the Earth's history are consistent with being caused by a devastating influx of radiation from space.

Threatening stars

"Direct proof that it happened this way is lacking at present," he said, "but many people are looking for it."

There is some good news! Because the gamma-ray bursts from collapsing supermassive stars are shot across the cosmos in narrow beams, probably no more than a degree across, most of them will miss the Earth.

However, the latest statistics suggest once every one hundred million years or so, we will be unlucky. Curiously, this is about the rate of global extinctions on Earth.

At the moment, astronomers do not know which star to watch. Stars, like the supermassive Eta Carinae, visible in the Southern Hemisphere, are likely to explode and send out a gamma-ray burst sometime in the next million years or so. But this particular star is not pointing in our direction.

Undoubtedly, there is a star that is, but as yet astronomers have not found it. But even if they do, will we get any warning?

"Not with our current understanding of science," said Dr Dar, "but then science progresses. Perhaps, one day we will be able to tell which stars are threatening."

See also:

28 May 98 | Sci/Tech
Cosmic clouds threaten Earth
28 Jan 99 | Sci/Tech
Scientists snap deep space blast
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