Abstract
The LIGO and the Virgo collaborations have recently announced the first detections of Gravitational Waves. Due to their weak amplitude, Gravitational Waves are expected to produce a very small effect on free-falling masses, which undergo a displacement of the order of 10-18 m for a Km-scale mutual distance. This discovery showed that interferometric detectors are suitable to reveal such a feeble effect, and therefore represent a new tool for astronomy, astrophysics and cosmology in the understanding of the Universe. To better reconstruct the position of the Gravitational Wave source and increase the signal-to-noise ratio of the events by means of multiple coincidence, a network of detectors is necessary. In the USA, the LIGO project has recently concluded its second Observation Run (O2) with a couple of twin 4 kilometer-long arms detectors which are placed in Washington State and Louisiana. Advanced VIRGO (AdV) is a 3 kilometer-long arms second generation interferometer situated in Cascina, near Pisa in Italy. The installation of AdV has been completed in 2016, and the first commissioning phase allowed to get to the target early-stage sensitivity, which was sufficient to join LIGO in the O2 scientific run. In this paper, the challenges of the commissioning of AdV will be presented, together with its current performances and future perspectives. Finally, in the last paragraph the latest discoveries that occurred after the ICNFP 2017 conference will be also described.
Highlights
Gravitational Waves (GW) are a perturbation of the flat space-time metrics due to the acceleration of masses
In order to join the second part of O2 scheduled for August 2017, the commissioning activity had to exploit this left only ten months to go from scratch to a decent sensitivity for Advanced Virgo
Advanced Virgo has shown a great stability during O2, reaching a very high duty cycle even higher than the two aLIGO detectors, with locking segments lasting up until 7 ̃0 hours
Summary
Gravitational Waves (GW) are a perturbation of the flat space-time metrics due to the acceleration of masses. They are foreseen by Einstein’s field equations of the General Relativity, which can be linearized in weak field approximation, giving rise to a wavy solution. The GW amplitude is proportional to the second time derivative of quadrupolar moment tensor through G/c4 ≈ 10−47 N−1. This number being very tiny, explains why only huge accelerated masses can give rise to detectable effects. Given two free-falling masses separated by a distance L, the effect induced by the GW can be estimated as: δL = hL (2).
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