In August 2025, the LIGO-Virgo-KAGRA (LVK) Collaborations released the interferometric strain data from the first part of the fourth observing run (O4a), which ran from May 2023 to January 2024. In this data, we have discovered 128 new confident gravitational-wave signals originating from merging black holes and neutron stars. Alongside the strain data release, we publish version 4.0 of the Gravitational Wave Transient Catalog (GWTC-4.0), which contains lists of the candidate signals and measurements of their properties.
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