VIRGO is an international collaboration for the detection of

1. Input Mode Cleaner Length = 144 m West mirror Arm Length = 6 m Recycling Laser Nd:YAG North mirror P=20 W P=2mW P=100mW Output Mode Cleaner Length = 4 cm Auxiliary laser Central Interferometer configuration The Mirror suspension: the super attenuator VIRGO is an international collaboration for the detection of Gravitational Waves • ITALY - INFN • Firenze • Frascati • Napoli • Perugia • Pisa • Roma • Urbino • FRANCE - CNRS • Paris • Lyon • Orsay • Annecy • Nice General relativity describes gravity as a manifestation of the curvature of space-time. This description has been tested in the solar system, where gravity is weak and changes slowly due to the orbital motions of planets and their satellites. Einstein's theory predicts the existence of gravitational waves, that is, perturbations of the gravitational field, which, as it is for electromagnetic field, spread out through space at the speed of light. Right from their source, these waves radiate, like ripples on the surface of a pond. Spreading out, the waves decrease very slightly when interacting with matter, thus, unlike electromagnetic radiations, they are not stopped either by the stars, nor by interstellar matter. VIRGO layout The Virgo project consists mainly in a Michelson laser interferometer made of two orthogonal arms being each 3 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 will be located at Cascina, near Pisa on the Arno plain. The frequency range of Virgo extends from 10 to 6,000 Hz. In order to reach the extreme sensitivity required, the whole interferometer should attain optical perfection and be completely isolated from the rest of the world in order to be only sensitive to the gravitational waves. To achieve it, Italian and French scientists involved in the project, are developing most advanced techniques in the field of high power ultrastable lasers, high reflectivity mirrors, seismic isolation and position and alignment control. Aerial view of VIRGO at Cascina (Tuscany in Italy) • VIRGO will permit scientists to test this theory for rapidly changing, dynamical gravity and also for the extremely strong, dynamical gravity of two black holes as they collide. • VIRGO has the possibility to: • Verify directly general relativity's prediction that gravitational waves exist and propagate • - at the same speed as light , thus the graviton has zero rest mass. • the forces the waves exert on matter are perpendicular to the waves' direction of travel, and stretch matter along one perpendicular direction while squeezing it along the other; • thereby, test general relativity's prediction that the graviton has twice the rate of spin as the photon. • Moreover it can firmly verify that black holes exist, and test general relativity's predictions for the violently pulsating space-time curvature accompanying the collision of two black holes. This will be the most stringent test ever of Einstein's general relativity theory. • Interferometer Control and • Data production • Fully digital control: robust on long periods • 20 kHz main signal acquisition • Data flow: 4 Mbyte/s The beam splitter in place: view from the bottom Central interferometer results • Best sensitivity:10-16 m/Hz1/2 @ 1 kHz • 10-13 m/Hz1/2 @ 10 Hz • 5 orders of magnitude gained in 1 year • Some of the main achievements: • Interferometer Control and reliability of VIRGO superattenuator • Locking force partition over two points (hyerarchical control) • Locking of the recycled CITF (lock acq. time: sec. to min.) • Automatic alignment • Local control noise reduction • Stable ISYS+CITF operation • Limiting noise identified over a large part of the spectrum • Sources of lock losses are identified • Integration of all subsystems achieved Duty cycles: 98%85%98%98%73% The 3 km vacuum of the North arm The Virgo Central area • VIRGO status: • - The vacuum system completed and within specifications • - The mirrors are in place • - VIRGO 3 km commissioning is starting in mid 2003 and it will benefit of the experimental results already obtained in the Central interferometer commissioning Sensitivity improvements of the central Interferometer of VIRGO Sensitivity goal of VIRGO The super attenuator Beam splitter paylaod assembly Beam light arriving at the North tube end Front view of the beam splitter