A historic milestone for Virgo and the global network
The LIGO-Virgo-KAGRA gravitational wave detector network has announced the detection of its 200th signalduring the fourth observation cycle (O4), active from May 2023 to April 2025. An astonishing achievement, especially considering that only 90 events had been detected across all previous cycles (O1, O2, O3).
This leap forward is thanks to significantly increased detector sensitivity, achieved through years of technological upgrades. Detecting extraordinary events like black hole mergers or neutron star collisions depends on the synchronous activity of the four major interferometers around the world: two LIGO detectors in the US, Virgo in Italy, and KAGRA in Japan.
A technical break… but only for the lasers
As of April, all four detectors entered a coordinated nine-week technical break, planning to resume observations in June and wrap up cycle O4 by October 7. The pause was initially triggered by the need to fix a faulty valve at LIGO Livingston before hurricane season, but it’s also the perfect chance to upgrade stability and sensitivity across the network.
At the Virgo site in Cascina, researchers are using the downtime to replace one of the main mirrors at the end of the western arm, compromised by a tiny speck of dust. A highly delicate operation that will take about a month to complete.
Public visits in full swing: Open Day on May 23
Despite the observation break, activity at the European Gravitational Observatory (EGO) is anything but paused. Maintenance allows access to usually restricted areas, and over 1,000 visitors each month explore Virgo’s facilities—including many school groups.
A special Open Day will be held on May 23, offering a behind-the-scenes look at the technology used to listen to the universe. It’s a unique opportunity for families, students and space enthusiasts to connect with the science of gravitational astronomy.
The next frontier: multimessenger events
The scientific community is eagerly waiting to witness another multimessenger event—an astronomical phenomenon observed not only via gravitational waves, but also through light, radio waves, gamma rays, and more. So far, this has only happened once, on August 17, 2017, with the merger of two neutron stars—a landmark moment in modern astronomy.
That’s why scientists work 24/7 during observation cycles, rapidly relaying preliminary data to a global network of over 100 observatories and telescopes, ready to point their instruments at the sky.
Virgo and the future of astronomy
“Gravitational astronomy is revolutionizing the way we observe the cosmos,” said Gianluca Gemme, Virgo spokesperson. The insights gained in just ten years have reshaped our understanding of stellar evolution and black hole populations.
With more than 900 scientists involved and funding from five European nations, Virgo remains a flagship of European research. And this current pause is just the prelude to more groundbreaking discoveries that might reveal even deeper cosmic secrets.
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