Virgo was the Italian gravitational-wave detector that joined LIGO in observing GW170814. Located near Pisa, Virgo contributed the third interferometer in the first confirmed three-detector observation of a binary black-hole merger.
GW170814 was detected on August 14, 2017, during the first joint observing period involving Advanced LIGO and Advanced Virgo. The two LIGO instruments were in Hanford, Washington, and Livingston, Louisiana; Virgo’s European location added a much longer baseline to the network. Comparing arrival times and waveform amplitudes across all three sites sharply improved the source’s sky localization.
The event was especially important because Virgo had only recently begun participating in observations. TAMA 300 and GEO600 are also gravitational-wave instruments, while KAGRA is Japan’s cryogenic detector, but none was the Italian observatory involved in GW170814. Virgo’s participation helped reduce the probable source region by more than an order of magnitude compared with the two-detector network.