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VIRGO Celebrates the End of Its Construction
Construction of Virgo, the large and impressive French-Italian gravitational wave detector, has just been completed, and the 3-km interferometer is now poised to enter the next stage in its development, full-scale commissioning. This new phase is scheduled for the end of July. We at LIGO fully expect that before long Virgo will attain running stability and strain sensitivity comparable to our own interferometers, and we look forward to the date when Virgo will join us in the search for gravitational waves. In anticipation, we have already begun joint LIGO-Virgo discussions as to the best method of data exchange between our detectors. This exchange has two goals: to strengthen the observations and analyses of both detector groups through reciprocal verification; and in the longer term, to move toward developing a worldwide network of gravitational wave detectors.
The end of its construction, and the start of commissioning of the full-scale Virgo, is an important milestone indeed. To mark the event, a gala inaugural was held July 23 in Cascina, Italy, where the Virgo detector is located. The celebration included tours of the facility, scientific speeches, participation by many important dignitaries from the French and Italian governments and funding agencies--and of course a never-ending supply of food, drink and good cheer.
The Virgo project is a collaboration between scientists from France and Italy, and has been jointly funded by the Centre National de la Recherche Scientifique (CNRS) of France, and the Istituto Nazionale di Fisica Nucleare (INFN) of Italy. As Virgo construction neared its end, the CNRS and INFN decided to create a new organization, the European Gravitational Observatory (EGO), that has now assumed responsibility for Virgo operations, and strives to foster gravitational wave research in Europe. A noteworthy development is that EGO has recently begun a new program to support Advanced R&D efforts in Europe for the benefit of future generations of gravitational wave detectors. This is an important and forward-looking advance in the future of our field in Europe.
EGO and its present director, Filippo Menzinger (pictured just below, at the inaugural), hosted the Virgo celebration, which was attended by about 350 guests. The morning activities included a set of tours, exhibition of an impressive new video entitled "Virgo: a New Window on the Universe," and a series of scientific presentations that included talks by D. Enard (pictured second below), Virgo technical manager, on an "Overview of the Construction Phase"; A. Brillet, joint Virgo project leader, on "VIRGO: from the Idea to Realization"; R. Barbieri, chairman of ApPEC Peer Review Committee, on "Astroparticle Physics: How and, Above All, Why"; B. Barish, Director of LIGO and former Chairman of GWIC, on "Virgo: Observing the Most Violent Events in the Universe"; M. Davier, Virgo Collaboration, LAL, Orsay, on "An Outlook on Gravitational Waves Research"; and finally a description by F. Menzinger, EGO Director, on "What is EGO?"
D. Enard traced the construction of Virgo from the civil development at the site to the implementation of the optics and the initial commissioning of the central interferometer. A special feature of Virgo is its suspension system, which consists of ten-meter-tall towers containing six sets of coupled inverted pendulums that damp horizontal movements, combined with six sets of springs and weights that damp vertical movements. The central interferometer system has already undergone extensive testing for about a year and now gives performance near design goals. The Virgo team hopes this experience will significantly shorten the commissioning time for the full-length interferometer.
The Virgo project began when Alain Brillet and Adalberto Giazotto came together at a meeting about 20 years ago and decided jointly to pursue the development of a large scale interferometer project with the low frequency technology, involving seismic isolation to be developed in Giazotto's laboratory, and the optical technology and ability at high frequencies in Brillet's laboratory. This collaboration evolved into the Virgo facility that was inaugurated on July 23.
When Virgo was originally conceived in the early 1980s, they had decided to name it after the Virgo Cluster, an agglomeration of about 1000 galaxies having enough stars to produce many supernovae (the gravitational collapse of a star that should emit gravitational waves). The original hope was to build a detector sensitive enough to record the gravitational waves from these exploding stars. This is still a goal of both Virgo and LIGO, but by present estimates it will require second generation detectors to attain the necessary reach. Of course the primary goal of Virgo, like LIGO, might be characterized simply as "to observe the most violent events in the universe," which includes the collisions of black holes, the gravitational collapse of stars, and even the relic signals from the big bang. Interestingly--and perhaps appropriately--Cascina, the location of Virgo, has long been associated with "violent events" due to a famous work by Michelangelo.
Michelangelo's piece on Cascina was inspired following the expulsion of the Medici in 1494, when the rebirth of the Florentine Republic was a moment of intense self-rediscovery for Florence. Following a century in which the city had become more like a conventional princedom, it was reasserting a republican government. Michelangelo was an enthusiastic supporter of this development and had high hopes for the revitalization of the Florentine government. He returned to Florence at that time and created his famous and seductive work of political art, the massive sculpture of David, hero of the weak against the strong (or of Florence against tyrannical powers).
Michelangelo was then commissioned to create what was expected to be a patriotic masterpiece in the Palazzo Vecchio. Unfortunately, he never completed the painting, but did manage to create a powerful full-size drawing of the piece, which he entitled the "Battle of Cascina." The images of war he depicted were not the expected bright and celebratory pageants of chivalry, but rather were enigmatic and disturbing. This full-size drawing has not survived, except in that it served as the main visual reference of a painting now in Holkham Hall, Norfolk, by Bastiano da Sangallo. Despite the fact that Michelangelo's "Battle of Cascina" was never completed, the image from the drawing (reproduced below) has long been considered one of the most haunting representations of the violence of war.
The tradition of associating Cascina with "violent events" that began so wondrously with Michelangelo has now been passed on in our time to our Virgo associates, who aim to follow that great tradition by observing a different type of violent events, those associated with the entire Universe. So we have evolved from the violence of war in the 16th Century to the violence of the Universe in the 21th Century.
At the inauguration, Alain Brillet presented the history of the project from its conception, sharing many of the technological achievements and milestones. Virgo is superficially much like LIGO. It is a large-scale (e.g. three-kilometer) suspended mass interferometer placed on a flat rural site. It does in fact have many similarities in design and implementation, and expects to achieve similar sensitivity for gravitational waves. It is fair to say that many of the ideas invented for Virgo, as pointed out by Brillet, have been incorporated into LIGO and the other long baseline interferometers. Of course, the reverse is also true: many advances developed for LIGO have been incorporated into Virgo. This healthy parallel development, which holds also for GEO, TAMA and AIGO, has collectively brought our field to the point where we can now anticipate having detectors capable of observing gravitational waves.
Yet in detail, Virgo and LIGO have different philosophies and optimizations. The most striking difference is that LIGO is built around having two facilities and using the combined observing power to detect gravitational waves. In LIGO, early universe signals are perceived from cross correlating signals from the two sites, while binary inspirals of compact objects are detected by asking for simultaneous detection (within a small difference due to the speed of light) at both sites. In contrast, Virgo is a single powerful detector optimized to extend the bandwidth to lower frequencies with a very sophisticated seismic isolation system. This will enable the observation of many more cycles for the merger of compact objects and a broader frequency band to search for signals from spinning pulsars.
The highlight of the afternoon activities was the presence of many high-ranking guests from both the Italian and French government and funding agencies, as well as senior leaders in science. The afternoon session included talks by S. Katsanevas, EGO Council President; E. Iarocci, INFN President; G. Berger, Directrice Generale du CNRS; A. Giazotto, Virgo Spokesman; and finally, from the French and Italian science ministers, C. Haignere', Ministre deleguee a la Recherce et aux Nouvelles Technologies of France; and L. Moratti, Ministro dell'Istruzione, dell'Universita' e della Ricerca of Italy.
The Virgo inauguration was a gala event, and a great kick-off for its next phase of work. The Virgo team expects to commission the full-scale interferometers over the coming year or so, and we anticipate that they will reach comparable sensitivity in the not-to-distant future. At that point, we will begin to exchange data. We all look forward eagerly to that time when Virgo joins us in the search for gravitational waves.
The similarities between LIGO and Virgo will permit their affiliated use in what we hope will evolve into a worldwide network of gravitational wave detectors. Such an alliance will improve our ability to distinguish gravitational wave events with confidence, help us to better localize the origination of events in the sky, and assist us to disentangle the two different components of gravitational wave signals. In his morning talk, M. Davier outlined a strategy of using different detectors in a worldwide network to gain better coverage of the sky, and more confidence in detections. In the afternoon, before the ministers and other government officials, Adalberto Giazotto emphasized the goals and importance of developing a worldwide network, as well as giving his vision of the means toward devising even more sensitive detectors, in particular developing his favorite scheme of making cryogenic interferometers to lower the thermal noise.
Let me conclude with a statement as Director of the LIGO Laboratory and also on behalf of the LIGO Scientific Collaboration (LSC) in giving our whole hearted congratulations to our colleagues in Virgo for their impressive accomplishments. We look forward to forging a strong partnership as we move into the future, one that will enable us to pursue this exciting field with the combined strengths of our groups and detectors. Finally, as outgoing chair of the Gravitational Wave International Committee (GWIC) with representation of all the major detectors, I offer the congratulations of the international community.