Virgo interferometer
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The Virgo is a gravitational wave detector in Italy, which commenced operations in 2007. It is one of a handful of the world's major experiments working towards the observation of gravitational waves.
Virgo is a massive Michelson laser interferometer made of two orthogonal arms, each three kilometers long.
Multiple reflections between mirrors located at the extremities of each arm extend the effective optical length of each arm up to 120 kilometers. Virgo is located within the site of EGO (European Gravitational Observatory) at Cascina, Italy.
The frequency range of Virgo extends from ten hertz to ten kilohertz. This range as well as the very high sensitivity should allow detection of gravitational radiation produced by supernovae and coalescence of binary systems in the Milky Way and in outer galaxies, for instance from the Virgo cluster.
In order to reach the extreme sensitivity required, the whole interferometer attains optical perfection and is extremely well isolated, in order to be only sensitive to the gravitational waves.
To achieve this, Italian and French project scientists have developed many of the current leading techniques in the fields of high power ultrastable lasers, high reflectivity mirrors, seismic isolation and position and alignment control.
Regarding optics, Virgo uses a new generation of ultrastable lasers, and the most stable oscillator ever built.
A specific optical coating facility was built to produce extremely high quality mirrors combining reflectivity over 99.999 %, with nanometer surface control.
To avoid spurious motions of the optical components due to seismic noise; each component is isolated by a 10 m high, very elaborate system of compound pendulums.
Because the presence of a residual gas would slightly perturb the measurements the light beam must propagate under ultra high vacuum. Indeed, the two tubes, 3 km long and 1.2 m diameter are the largest ultra high vacuum vessels in Europe and the second largest in the world.
The environment of the Virgo interferometer is quieter than that of a spacecraft orbiting the earth.
Virgo, the construction of which was completed in June 2003, started its first science run in May 2007 and it is currently running day and night listening for any and all gravitational signals which may arrive at any time from any part of the Universe. The signals are detected, recorded and pre-analysed through an on-line computing system. These data will then be made available to the scientific community for further analysis.
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Coordinates: 43°37′53″N 10°30′18″E / 43.63139°N 10.505°E
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