The LIGO, Virgo, and KAGRA collaborations have finished their fourth observation campaign, known as O4, marking the longest and most comprehensive period of coordinated gravitational wave monitoring to date. Initiated in May 2023 and spanning more than two years, the campaign involved simultaneous data analysis and resulted in the detection of 250 new gravitational signals, which account for mor Berlin, Germany (SPX) Nov 19, 2025
The LIGO, Virgo, and KAGRA collaborations have finished their fourth observation campaign, known as O4, marking the longest and most comprehensive period of coordinated gravitational wave monitoring to date. Initiated in May 2023 and spanning more than two years, the campaign involved simultaneous data analysis and resulted in the detection of 250 new gravitational signals, which account for more than two-thirds of all signals recorded by these observatories to date.
Improvements in detector technology and sensitivity enabled this increase in the number of observed events. Data from the latest run contributed to major advances in the understanding of compact binary systems and fundamental processes in the universe. Key discoveries were announced and published as the campaign progressed.
"The completion of O4 marks a historic milestone: the longest observing run ever conducted by the global gravitational-wave network," stated Gianluca Gemme, spokesperson for the Virgo Collaboration and researcher at the Italian National Institute for Nuclear Physics (INFN). "Virgo has played a crucial role, contributing to the detection and characterization of numerous signals. The success of the O4 run reflects the strength of international collaboration and the relentless effort of our teams to push the boundaries of such precise and challenging measurements. Looking ahead, we are preparing for major upgrades that will significantly enhance the sensitivity of our detectors, ensuring a new and even greater scientific impact."
Among the analyzed events, GW250114 enabled scientists to observe two black holes merging with unprecedented accuracy and provided data supporting Stephen Hawking's prediction that the total surface area of black holes cannot decrease during mergers. In this instance, the total area increased from 240,000 to about 400,000 square kilometers.
Other outcomes include the detection of "second generation" black holes - events GW241011 and GW241110 - defined by unusual mass and rotational features likely resulting from preceding mergers in dense cosmic environments. Additionally, GW231123 stands out as the most massive black hole merger identified so far, yielding a black hole over 225 times the mass of the Sun, posing challenges to existing models of stellar evolution.
Further results from the hundreds of collected events are in progress. A comprehensive catalogue of the O4 campaign is planned for release in the coming months.
Preparations are underway for major technological upgrades to the detectors, set to occur in stages that will include intervals of data collection. The next observation campaign is scheduled to begin in late summer or early autumn of 2026, lasting approximately six months.
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