The Gravitational-Wave Transient Catalogue-4.0 (GWTC-4) marks a significant milestone in our understanding of the Universe, presenting 128 new events detected by the LIGO-Virgo-KAGRA collaboration from May 2023 to January 2024. This extensive compilation provides insights into diverse binary systems, enhances our understanding of black hole formation and cosmic evolution, and offers an additional method to validate the theory of general relativity.
Viola Sordini, a researcher at IP2I Lyon and deputy spokesperson of the Virgo Collaboration within the LIGO-Virgo-KAGRA (LVK) network, discusses the findings from the catalogue and the implications of advancing our understanding of gravitational waves for fundamental physics and the Universe.
Gravitational waves (GWs) help us understand the Universe in two ways: (1) because of the information they carry as messengers, and (2) simply because they exist!
The LIGO-Virgo-KAGRA collaboration has reported more than 200 confirmed gravitational-wave signals, emitted by binary systems of black holes and/or neutron stars. The GWTC-4 dataset includes only gravitational-wave signals collected during the first third of the fourth LIGO-Virgo-KAGRA observing run. Additional data from subsequent observations are scheduled for release on May 26 and December 16, 2026, and are expected to approximately double the number of confirmed detections.
The event GW231123 was generated by the merger of two black holes of approximately 100 and 140 times the mass of the Sun, making it the most massive binary system observed by the LVK so far. Black holes in this mass range are difficult to form through standard stellar evolution alone and may instead be the result of previous mergers.
The event GW231028 also has a high total mass of about 150 times the mass of the Sun and exhibits one of the strongest and most confidently measured spin alignments.
The data from GWTC-4 enable more stringent tests of general relativity and confirm its excellent agreement with the data. They also place strong constraints on alternative theories predicting possible deviations.
The findings from GWTC-4 play a role in measuring the expansion rate of the Universe. A GW signal from a compact binary coalescence carries the information of the luminosity distance of the source.
The LIGO-Virgo-KAGRA collaboration has been able to measure H0 with increased precision compared to previous analyses.
The improvement in detector sensitivities has a direct impact on the success of the fourth observing period. These improvements come from a continuous effort of the observatories’ teams to better understand and reduce noise sources.
The LVK has learned important operational lessons from the production of GWTC-4, in particular in terms of coordination and organisation. The network is now moving towards an even more integrated global scientific collaboration, called IGWN (International Gravitational-Wave Observatory Network).
