RIPPLES in the fabric of space-time caused by cataclysmic events deep within our Galaxy may have been picked up on Earth. If the results are confirmed, it will give astronomers an entirely new way to look at the Universe.
Einstein predicted the existence of ripples in space-time, or gravitational waves, in his general theory of relativity in 1915. The waves should pour out of hugely energetic events 鈥� such as exploding stars 鈥� at the speed of light and carry unique information on the events that produced them across vast stretches of space. Detecting them could help firm up our understanding of gravity and reveal astronomical oddities such as colliding black holes that might otherwise be completely undetectable. But so far the waves have eluded scientists.
Now, there are hints that a team of Italian researchers led by Eugenio Coccia of the INFN Frascati National Laboratories and Rome University has detected them. 鈥淭his will be a really big deal if it鈥檚 correct,鈥� says David Blair, an expert on gravitational waves at the University of Western Australia in Perth. 鈥淚f we can detect gravitational waves, we鈥檒l be able to listen to the Universe as well as see it,鈥� he says. 鈥淭hese detectors will be like bionic ears for the human race.鈥�
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The Italian team used two detectors. The first, known as EXPLORER, is a 2.3-tonne aluminium bar based at CERN, the European centre for particle physics near Geneva. The other is NAUTILUS, an identical bar at the Frascati lab.
To look for gravitational waves, the scientists constantly monitor vibrations in the bars. The waves should stretch and squeeze the bars a tiny amount, effectively making them 鈥渞ing鈥�. To cut down vibrations from other sources, the bars are suspended on dampers and cooled to near absolute zero to quell thermal noise.
If identical bursts of vibrations are recorded at both Geneva and Frascati at the same time, it could be because a gravitational wave has just hit. And the signal from a gravitational wave should be strongest when the sides of the bars face the source of the wave.
Coccia鈥檚 group found that matching bursts of vibrations were most likely to be recorded when the sides of both of the bars faced into the Milky Way 鈥� which is exactly where most nearby sources of gravitational waves should be lurking. Coccia says the results hint that their detectors are hearing cataclysmic events in our own Galaxy.
If the signals do prove to be gravitational waves, they are very common. There could be tens of invisible objects, such as black holes and neutron stars, slamming into each other in the galaxy every year, says Coccia. The team鈥檚 report appears in the journal Classical and Quantum Gravity (vol 19, p 5449) and is posted at .
Blair cautions that the result might be a mirage. Fluctuations in power across European electrical grids might trigger signals in both detectors simultaneously, for instance. Despite the team鈥檚 efforts to cancel vibrations from other sources, the data will still be very noisy, Blair says, making it hard to judge the statistical significance of their results.
Similar findings have been reported before. For instance, the Italian team鈥檚 founder, Guido Pizzella, reported possible gravitational waves from a supernova in a nearby galaxy in 1987. However, none of these claims was ever confirmed. 鈥淏ut this should definitely not be dismissed out of hand,鈥� Blair says. 鈥淢any people are quick to criticise others for digging deep into their data. The climate of opinion is such that you have to be rather brave to do it. I applaud the Italians for persisting in these attempts.鈥�
Coccia points out that the detectors are 10,000 times as sensitive as they were in 1987. However, he is first to admit that his team and other detectors need to gather more data before they can confirm the result. By the end of next year they hope to have collected enough data to remove any doubt.
鈥淚f this turns out to be real, we鈥檒l be very proud and happy,鈥� says Coccia. 鈥淪ome people have been working on this for 30 years and it would be the realisation of our dreams.鈥�
