5 March 2026 — The new gravitational-wave catalog from the international LIGO (USA), Virgo (Italy), and KAGRA (Japan) network is now online: the Gravitational Wave Transient Catalogue 4.0 (GWTC-4). The result of more than two years of analysis, it collects 128 new events observed between May 2023 and January 2024 (observing run O4a), more than doubling the number of signals from previous campaigns. The wealth of data reveals an unprecedented variety of binary systems that generate gravitational waves and provides key tools to understand the origin of black holes, cosmic evolution, and to test general relativity with increasing rigor.
Among the results, several events stand out: GW231123 (the designation indicates the year, month, and day of observation), the most massive binary black hole system ever detected with this technique (about 130 solar masses each), likely the product of hierarchical mergers in dense stellar environments; GW231028, in which both black holes have exceptionally high spin (the two celestial bodies rotate at speeds up to ~40% of the speed of light); and GW231118, characterized by the largest mass asymmetry ever observed. The catalog also includes two mixed black hole–neutron star systems, broadening the range of known sources.
These new measurements, even more precise than those from previous observing campaigns, allow increasingly stringent tests of Einstein’s theory. Analyses of particularly clean signals, such as GW230814, show no deviations from general relativity in the dynamic, strong-field regime. At the same time, by treating the events as “standard sirens,” the LVK collaboration obtains a new independent estimate of the Hubble constant: about 76 km/s per megaparsec, an important contribution to the ongoing debate about the expansion rate of the Universe.
The GWTC-4 catalog, accompanied by a series of papers in Astrophysical Journal Letters and by publicly released data for the scientific community, represents a true kaleidoscope of cosmic collisions and a major step forward for gravitational-wave astronomy. With the next observing phases, the map of black-hole mergers will become even clearer, paving the way for tests of fundamental physics and for new cosmological measurements.
Reference: A. G. Abac et al. 2025, ApJL 995 L18, DOI: 10.3847/2041-8213/ae0c06
Attached graphic material: GWTC-4 infographic.
Each panel represents the time-frequency signature of a single event, namely the merger of two black holes, two neutron stars, or one of each. The events are organized by observing runs, highlighted in different colors. In the first run (O1) 3 signals were detected; O2 observed 8 events; and O3 observed 79. The first part of the fourth observing period (O4a) includes 128 new events. Therefore, the Gravitational-Wave Transient Catalog 4.0 contains 218 events detected over the past decade.
Credits: Ryan Nowicki / Bill Smith / Karan Jani
Additional material:
https://www.youtube.com/watch?v=3B6WKSWDJRE&t=7s
The visualization shows simulations of binary black hole mergers for the 86 events analyzed in detail in the GWTC-4.0 catalog.
