Status of Advanced Virgo and upgrades before next observing runs

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].