25 Aug 2025
blog
Today we’re announcing that we’ve more-than-doubled the number of black hole collisions which we’ve observed using gravitational waves. We’re also releasing an enormous amount of data collected between May 2023 and January 2024 which measures tiny changes in the Universe’s geometry measured by gravitational-wave detectors, which are how we identify these collisions.
We collect the information about these collisions into publications which we call a “catalog”, which contain all of the information we’re able to extract from the signals we detect and interpret. This includes things like the mass of the objects which were colliding, how fast they were spinning, and whereabouts in the Universe they were.
We’ve published earlier versions of this catalogue before now: GWTC-1.0 has events from the first two observing-runs, GWTC-2.0 adds events from the first part of the third observing-run, and GWTC-3.0 events from the second part of that run. GWTC-4.0, which we’ve released today on the arXiv, is the latest version, analysing the first part of our fourth observing run (O4a). The amount of information in these has become so large that we now split the publication describing the catalog into three parts: an introduction paper, a paper describing the methods used in the analyses, and the results of those analyses.
I’ve had the pleasure of leading a team which performed one of these analyses (the “parameter estimation” analysis), which takes signals which have been identified in the data and then works out the properties of the black holes and neutron stars which produced them. It took around 60 of us to do this (and there’s more about that later in this post). I then took-over as the editor of the results part of the catalog publication in June. It’s quite nice to know that I’ve joined a bit of a Glasgow tradition of doing this: my line-manager John Veitch was responsible for GWTC-2.0, and my colleague Christopher Berry for GWTC-3.0. I can only apologise to either of them if I ever thought they seemed to have an easy job!
