page_title: Virgo interferometer
section_title: Detector sensitivity
hierarchical_section_title: Virgo interferometer / Interferometric detection of a gravitational wave / Detector sensitivity
caption_attribution_description: English: One of the best Virgo sensitivity curves achieved in 2011
context_page_description: 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 in Santo Stefano a Macerata, near the city of Pisa, Italy.
  Virgo is part of a scientific collaboration of laboratories from six countries: Italy and France, the Netherlands, Poland, Hungary and Spain. Other interferometers similar to Virgo have the same goal of detecting gravitational waves, including the two LIGO interferometers in the United States. 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 and they are looking for signals which are weak, infrequent, one-time events, simultaneous detection of a gravitational wave in multiple instruments is necessary to confirm the signal validity and to deduce the angular direction of its source.
context_section_description: A detector like Virgo is characterized by its sensitivity, a figure of merit providing information about the tiniest signal the instrument could detect—the smaller the value of the sensitivity, the better the detector. The sensitivity varies with frequency as each noise has its own frequency range. For instance, it is foreseen that the sensitivity of the advanced Virgo detector be ultimately limited by:
  seismic noise (any ground motion whose sources are numerous: waves in the Mediterranean sea, wind, human activity for instance the traffic during daytime, etc.) in the low frequencies up to about 10 Hertz (Hz);
  the thermal noise of the mirrors and their suspension wires, from a few tens of Hz up to a few hundreds;
  the laser shot noise above a few hundreds of Hz.
  Virgo is a wide band detector whose sensitivity ranges from a few Hz up to 10 kHz. Mathematically speaking, its sensitivity is characterized by its power spectrum which is computed in real time using the data recorded by the detector. The curve opposite shows an example of a Virgo amplitude spectrum density (the square root of the power spectrum) from 2011, plotted using log-log scale.
caption: A sensitivity curve from the Virgo detector in the frequency band [10 Hz; 10 kHz], computed in August 2011"Virgo Sensitivity Curves". 2011. Archived from the original on 1 December 2015. Retrieved 15 December 2015.. Its shape is typical: the thermal noise of the mirror suspension pendulum mode dominates at low frequency while the increase at high frequency is due to the laser shot noise. In between these two frequency bands and superimposed to these fundamental noises, one can see resonances (for instance the suspension wire violin modes) such as contributions from various instrumental noises (among which the 50 Hz frequency from the power grid and its harmonics) which one is trying to reduce continuously.
exif: {}