Status of Advanced Virgo and upgrades before next observing runs

Abstract The upgrade to the second generation of ground-based gravitational waves detectors, finally allowed in 2015 the first direct detection of a Gravitational Wave, thus opening a new window of observation on the Universe. This outstanding achievement was the result of many years of joint research and development (R&D) efforts by the LIGO and Virgo collaborations. Since then, during the observing runs O1, O2 and O3 , many other events have been detected by both Virgo and LIGO (Laser Interferometer Gravitational-Wave Observatory). Since April 2020, right after the end of the O3 run, Advanced Virgo has undergone a period of instrument upgrade, still in progress, before the next observing run at present scheduled to start in mid-2022. This paper, after a brief introduction on Gravitational Wave detection, will provide an overview about Advanced Virgo design, its status and the planned instrument upgrades to the Advanced Virgo+ design, which will push the detector sensitivity towards the maximum achievable limit that is a detection range for compact binary neutron stars of 100 Mpc during O4 and 260 Mpc during O5 (2025-2026) [1].