Record haul of gravitational waves

The LIGO–Virgo–KAGRA (LVK) Collaboration has released GWTC-4.0, the latest Gravitational-Wave Transient Catalog, revealing a surge of new detections that is expanding the known population of black holes and neutron stars. These signals, generated by violent cosmic collisions, have travelled billions of years across spacetime to reach Earth.

This major release includes 128 new gravitational-wave candidates identified during the first part of the fourth observing run, spanning May 2023 to January 2024. This single nine-month period more than doubles the number of detections from the previous three observing runs combined, which together yielded 90 events. The increase reflects significant upgrades in detector sensitivity and advances in analysis techniques, allowing LIGO’s interferometers to detect binary neutron star mergers at distances of up to a billion light-years.

The new catalogue extends the known range of gravitational-wave sources, uncovering systems that are more massive and more rapidly spinning than previously observed. One notable example is GW231123_135430, a binary black hole merger in which each component is estimated to be more than 100 times the mass of the Sun. Such systems may represent second-generation black holes, formed from earlier mergers. Another striking event, GW231028_153006, involves black holes spinning at around 40 percent of the speed of light.

These detections also provide powerful tests of fundamental physics. The particularly strong signal from another event, GW230814_230901, has enabled new, stringent tests of general relativity, which continues to agree with observations. In addition, gravitational-wave events can act as ‘standard sirens’ for measuring cosmic distances. Using this approach, researchers derive an independent estimate of the Hubble constant of 76 kilometres per second per megaparsec, adding an important data point to the ongoing debate over the Universe’s expansion rate.

“Each new gravitational-wave detection allows us to unlock another piece of the Universe’s puzzle in ways we couldn’t just a decade ago,” says Lucy Thomas, leader of the catalogue’s analysis and a postdoc at the Caltech LIGO Lab.

As the international detector network continues analysing data from later stages of the fourth observing run, gravitational-wave astronomy is moving beyond the first detections into an era of population studies. With growing numbers of events, astronomers are beginning to build a statistical picture of how black holes and neutron stars form and evolve across cosmic time.

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iopscience.iop.org/article/10.3847/2041-8213/ae0c06