Virgo Begins Scientific Study Of Gravitational Waves (7/21/2007)

On 18 May 2007, the VIRGO interferometer began its first phase of scientific operation. This is a crucial step in the hunt for gravitational waves. VIRGO, which is the largest European (French-Italian) detector, joins company with the LIGO detectors in the US. This ultra-high-performance array of observation instruments will in particular be able to observe the coalescence of binary black holes in distant galaxies and provide information about the direction of the source. VIRGO is jointly run by CNRS and Italy's National Institute for Nuclear Physics (INFN).

Gravitational waves, which are predicted by the theory of general relativity, are deformations in space-time. They are produced by violent astrophysical phenomena in our galaxy and well beyond it, for example by supernova explosions or the coalescence of two dense bodies, such as black holes or neutron stars. Until now, only indirect evidence of the emission of gravitational waves has been observed (for which the 1993 Nobel Prize was awarded). The first direct observation will open up the field of gravitational astronomy, and will enable us to improve our understanding of gravity and general relativity.

Now that VIRGO has begun its first phase of scientific operation, on 18 May 2007, this has become a real possibility. VIRGO operates day and night, continuously listening out for gravitational waves coming from the nearby Universe (out as far as the Virgo galaxy cluster, hence the name). A team of operators and scientists operates and monitors the instrument 24 hours a day, 7 days a week. The signals are detected, recorded and undergo a preliminary analysis with the help of an on-line computer system. The data is then made available to the scientific community for more thorough study at a later date.

The VIRGO gravitational wave detector is basically a Michelson laser interferometer made up of two perpendicular arms 3 kilometers long. Light travels several times between two mirrors located at the ends of each arm, and then combines with light from the other arm, where the waves interfere. Gravitational waves should show up as expansions and contractions of the distance between the mirrors of each arm (and by a change in interference) of around a billionth of the diameter of an atom (10-18 meter). In order to detect such tiny changes, the detector uses the most advanced technologies in the fields of metallurgy, optics, monitoring systems, vacuums, computers, data analysis, etc. The CNRS laboratories in Annecy, Lyon, Nice, Orsay and Paris play a major role in VIRGO and in the EGO consortium (jointly funded by CNRS and INFN), which hosts and runs VIRGO.

The VIRGO teams have linked up with scientists at LIGO in the US, and GEO in the UK and Germany, with the aim of joining forces in the hunt for gravitational waves. Pooling data will increase the chances of detecting the first gravitational waves, and will provide more information about the location of the source. The joint analysis of the data will be carried out as if the data came from a single detector made up of several sensors located on both sides of the Atlantic and on the Pacific east coast.

Note: This story has been adapted from a news release issued by The Centre National de la Recherche Scientifique

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