VIRGO

The Virgo experiment

Founding countries   Countries which have joined the Virgo experiment later
Formation	1993
Type	International scientific collaboration
Purpose	Gravitation wave detection
Headquarters	EGO
Location	Cascina
Coordinates	43°37′53″N 10°30′16″E / 43.6313°N 10.5045°E / 43.6313; 10.5045Coordinates: 43°37′53″N 10°30′16″E / 43.6313°N 10.5045°E / 43.6313; 10.5045
Region	Italy
Fields	Basic research
Membership	CNRS (France), INFN (Italy), NIKHEF (Netherlands), POGRAW (Poland) and RMKI (Hungary)
Spokesperson	Fulvio Ricci
Affiliations	LVC (LIGO Scientific Collaboration and Virgo Collaboration)
Budget	About ten million euros per year
Staff	More than 320 people contribute to the Virgo experiment
Slogan	Listening to the cosmic whisper
Website	www.virgo-gw.eu

The Virgo interferometer is a large interferometer designed to detect gravitational waves predicted by the general theory of relativity. Virgo is a Michelson interferometer that is isolated from external disturbances: its mirrors and instrumentation are suspended and its laser beam operates in a vacuum. The instrument's two arms are three kilometres long and located near Pisa, Italy.

Virgo is part of a scientific collaboration of laboratories from five countries: France and Italy (the two countries behind the project), the Netherlands, Poland and Hungary. Other interferometers similar to Virgo have the same goal of detecting gravitational waves, including the two LIGO interferometers in the United States (at the Hanford Site and in Livingston, Louisiana). Since 2007, Virgo and LIGO have agreed to share and jointly analyze the data recorded by their detectors and to jointly publish their results. Because the interferometric detectors are not directional (they survey the whole sky) and they are looking for signals which are weak and infrequent, simultaneous detection of a gravitational wave in multiple instruments is necessary to confirm the signal and determine its origin.

The interferometer is named for the Virgo Cluster of about 1,500 galaxies in the Virgo constellation, about 50 million light-years from Earth. As no terrestrial source of gravitational wave is powerful enough to produce a detectable signal, Virgo must observe the Universe. The more powerful the detector, the further it can see gravitational waves, which then increases the number of potential sources. This is relevant as the violent phenomena Virgo is potentially sensitive to (coalescence of a compact binary system, neutron stars or black holes; supernova explosion; etc.) are rare: the more galaxies Virgo is surveying, the larger the probability of a detection.