Completion of LIGO-Virgo-KAGRA’s Fourth Observing Run

The LIGO-Virgo-KAGRA Collaboration has concluded its fourth observing run (O4), which began on May 25, 2023, 12:00 AM JST and ended on November 19, 1:00 AM JST. During this period, the collaboration detected approximately 300 significant gravitational-wave signals. Papers reporting on the first 128 events observed during the initial eight months have already been published [1].

In O4, KAGRA operated from May 25 to June 21, 2023,  and transitioned to sensitivity improvement work. Unfortunately, the Noto Peninsula earthquake on January 1, 2024, caused severe damage to many vibration isolation systems for the mirrors. Recovery efforts were completed by autumn 2024, and further sensitivity upgrades continued. KAGRA resumed O4 observations on June 12, 2025. During the difficult period following the earthquake, we received many messages of encouragement and generous donations. We would like to express our sincere gratitude once again.

After O4, LIGO, Virgo, and KAGRA will enter a maintenance and upgrade phase to improve their performance. The next observing run (O5) is currently planned to start in 2028, but discussions are underway about the possibility of a shorter observing run of up to six months in 2026. In addition, detailed announcements of gravitational-wave events detected since 2024 are scheduled for 2026.

We look forward to your continued interest in the exciting progress of gravitational-wave astronomy.

Links

[1] GWTC-4.0 Catalog: https://gwcenter.icrr.u-tokyo.ac.jp/gravitational-wave-science/gwtc-4-0