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LIGO begins test run

21 Feb 2003

The gravitational wave detector LIGO is being put through its paces during an eight-week test phase.

Scientists in the US have just switched on LIGO, the Laser Interferometer Gravitational-Wave Observatory, for a test phase lasting eight weeks. During this period, researchers will test the system's data gathering capabilities and analysis techniques.

LIGO is a USD 300 million project that aims to detect gravitational waves, ripples in the fabric of space-time, caused by cosmic events. A six-month run is scheduled to begin this fall, which experts say will mark the true beginning of the search for this elusive phenomenon.

LIGO itself consists of three massive interferometers: two at Hanford in Washington State, US and the third in Louisiana, US. During the current run, all three will operate in unison as a single observatory.

The arms of the LIGO interferometers are 4 km long. When gravitational waves pass through LIGO's L-shaped arms, they will decrease the length of one arm while increasing the other. These changes will be tiny: just 10-16 cm.

A similar interferometer called GEO600 exists in Hanover, Germany. Jim Hough, a leading member of the GEO team based in the UK told Optics.org that he hopes GEO will be able to join the current LIGO run by the end of March. "This will allow us to test out the data exchange processes between the detectors," he explains.

This will not be the first time that the two systems have operated concurrently. LIGO and GEO took data together for 17 days in January 2002 and again in September. "These data have been analyzed and the first results have just been released at the American Association for the Advancement of Science meeting in Denver," Hough said.

These results show the so-called "upper limits" of LIGO. Hough explains that the upper limits indicate the sort of events that LIGO could detect. "These are the upper limits to the radiation that could be measured by the detector from sources such as supernovae, pulsars and the stochastic background," he said. "You can see anything above these levels, but not below."

But the big question is, do the scientists expect to see anything during this run? "I don't think we expect any discoveries this time," Hough said. "In the autumn, LIGO and GEO will team up for a 6 month run and I think that's when the real interest will start."

Jacqueline Hewett is news reporter on Optics.org and Opto & Laser Europe magazine.

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