The discovery of gravitational waves, predicted a century ago by Einstein in the context of the general relativity, has been a breakthrough in astronomy and it was recognized by the 2017 Nobel Prize in Physics. On September 14th 2015, a gravitational-wave crossing the Earth was detected by the two LIGO instruments, located 3000 km apart, and produced a signal equivalent with the displacement of 10-18 of the mirrors. The source was a merger of two black-holes at a distance of a billion light years. This first detection not only confirmed the Einstein theory, sweeping away the doubts of Einstein himself about their existence, but also demonstrated the existence of black-hole binaries and the possibility for them to merge.
Gravitational-wave astronomy thus began with the first detection by LIGO 2015, followed by the LIGO-Virgo detections made between 2017 and 2020. Today (summer 2021), about 50 gravitational-wave sources have been detected, mostly binary black-hole mergers, but also neutron star mergers, and also mixed pairs of black-holes and neutron stars.
LIGO and Virgo are currently being improved and, starting from the next data taking, planned in 2022, the LIGO-Virgo network will be expanded with the participation of KAGRA in Japan and LIGO in India.
ILANCE will foster new collaborations in the area of gravitational waves between CNRS/IN2P3 and the University of Tokyo. The long-standing experience acquired with the operation of Virgo and Advanced Virgo can benefit KAGRA through staff exchanges. On the other hand, KAGRA tests technologies as cryogenics, which are so far not used in Virgo and LIGO, but are considered for the future project of Einstein Telescope.
Topics for possible collaborations are on hardware development, exchange of software and data analysis and commissioning expertise: One example of the collaboration topic is on high quality mirrors. In the topic of data analysis, collaboration of groups between VIRGO and KAGRA lead the search for gravitational-wave bursts produced by cosmic strings using LIGO-Virgo data. In the future, exchanges of methods and tools to characterize and monitor the detector’s data quality are expected to grow. Future collaborations will also include exchange and exploitation of scientific data, in the framework of the LIGO-Virgo-KAGRA network and the development of innovative data analysis techniques. In the topic of calibration of gravitational-wave antennae, two independent methods are being developed: photon calibrators and Newtonian calibrators. Exchanges of hardware and colleagues visits to discuss and help on the different implementations of calibration methods will be of benefit for the network calibration. Another example of on-going collaboration between VIRGO and KAGRA is R&D for the broadband quantum noise reduction using filter cavities.
KAGRA PROJECT https://gwcenter.icrr.u-tokyo.ac.jp/en
LIGO EXPERIMENT https://www.ligo.org
Virgo Project https://www.virgo-gw.eu