The history of Virgo is an exemplary case: the Virgo concept, was prepared in 1987 by its two founding fathers, the Italian Adalberto Giazotto and the French Alain Brillet and was submitted in 1989 to the funding agencies. It was approved by CNRS and INFN in 1993-1994, the construction started in 1997. EGO was founded on the 11th of December 2000. The inauguration and commissioning started in 2003 and the scientific observations (runs) in 2007. Meanwhile the Netherlands laboratory NIKHEF joined the consortium in 2006 as an observer and an agreement was signed in 2007 for a common operation of Virgo with the LIGO detectors in the US, as a “single machine”. The upgrade of the machine to “Advanced Virgo” was approved in 2009 and was implemented till 2017.
Gravitational waves are a consequence of the theory of General Relativity (Albert Einstein, 1916) and they are ripples in the fabric of the space-time that propagate at the speed of light, and are produced when huge masses are accelerated or deformed. This happens in many astrophysical scenarios, including the mergers between black holes and/or neutron stars or supernova explosions. Gravitational waves are completely different from light, the main “messenger” used so far to study the Universe.
With the first detection of gravitational waves from the merging of two black holes at 1,4 billion light years, by the LIGO and Virgo collaborations in September 2015, a new window on the Universe had been opened, allowing to probe extreme phenomena driven by gravity.
The detection, announced in 2016, was rewarded “almost immediately” by the Physics Nobel prize of 2017 to R. Weiss, K. Thorn and B. Barish.
In August 2017 Virgo completed its upgrade and entered in the network with a sensitivity slightly lower than this of the US detectors. Nevertheless, two weeks later, on August 14th, the Advanced Virgo and Advanced LIGO interferometers detected a GW signal from the coalescence of two stellar mass black holes. The fact that the three interferometers detected the signal allowed to identify by triangulation the region of the sky where the event occurred with unprecedented precision. This detection inaugurated the era of gravitational wave astronomy.
Three days later, on August 17th, 2017 the first neutron star merger observed in coincidence in the LIGO and Virgo detectors triggered within few hours after the event had been recorder a follow-up campaign with about a hundred of observatories around the world detecting signals using messengers ranging from the high energy photons, to the visible light and radio waves. The concomitant observation of the merger in electromagnetic and gravitational waves was called the dawn of the multi-messenger astronomy with gravitational waves.
For this detection, Virgo has been named a historical milestone by the worldwide Institute of Electrical and Electronic Engineers (IEEE), and a dedication ceremony will happen in 2020. Virgo is thus joining the achievements of Benjamin Franklin, Volta, Marconi and others.
At the end of 2018, 10 a catalogue containing 10 binary black hole coalescences was published. During the observation period started in April 2019 and suspended in April 2020, there were 56 alarms of binary coalescences involving black holes and neutron stars , in the process of publication. These and other signals, including undetected signals so far, e.g. continuous gravitational wave emission from cosmic sources, supernova explosions and other cosmological events are in the process of revolutionizing fundamental science through developing synergies with cosmology, particle, nuclear, astroparticle physics and astrophysics.
This is why the Gravitational wave detection has been rightly called a scientific revolution comparable to that of Galileo pointing his telescope to the sky.
The historic beginnings of Virgo:
- A. Giazzoto, “Interferometric detection of gravitational waves”(Pysics Report, 1989)
- A. Brillet, A. Giazotto et al.,“VIRGO Proposal for the construction of a large interferometric detector of gravitational waves”(1989)
- A. Brillet, A. Giazotto et al.,“VIRGO Final Concept Design”(1992)