Artistic representation of a binary black hole merger. In cases like GW241011 and GW241110, where at least one black hole rotates in a peculiar direction relative to the orbital plane, the unusual spins offer hints about how the system formed. Credit: Carl Knox, OzGrav, Swinburne University of Technology
Gravitational waves - ripples in the fabric of space and time - are produced by some of the most violent events in the cosmos: black holes colliding, neutron stars smashing together, billions of light-years away. First detected in 2015, scientists can now pick up these signals using a global network of extraordinarily sensitive detectors.
The international LIGO-Virgo-KAGRA (LVK) Collaboration has today published the Gravitational Wave Transient Catalogue 5.0 (GWTC-5), adding 161 newly detected signals collected between April 2024 and January 2025.
That brings the grand total of confirmed detections to 390 - a figure that would have seemed extraordinary a decade ago. When active, the detectors pick up three or four signals every single week.
Scientists from the University of Portsmouth's Institute of Cosmology and Gravitation (ICG) have played a role in the LVK Collaboration, contributing to data analysis, cosmology and studying the population of black holes.
Our results are steadily getting better and better, which paints a really exciting picture for the future of cosmology."
Professor Tessa Baker, Institute of Cosmology and Gravitation
Professor Tessa Baker , from the University of Portsmouth's ICG, said: "I've been part of the team using these gravitational-wave detections to measure the most important number in cosmology: the expansion rate of the universe. Our results are steadily getting better and better, which paints a really exciting picture for the future of cosmology."
On 15 June 2024, a signal called GW240615 was detected simultaneously by detectors in the US and Italy. Using data from all three detectors, scientists were able to trace the signal back to a patch of sky just 6 square degrees across - a new record.
Knowing where to look is crucial for pointing other telescopes at the same region to detect any light the event may have produced. The signal originated from two black holes weighing around 26 and 30 times the mass of our Sun, colliding more than 3 billion light-years away.
A signal detected on 14 January 2025 - known as GW250114 - is the sharpest gravitational wave ever observed. It was produced by two near-identical black holes (32 and 34 solar masses) merging more than a billion light-years from Earth.
The exceptional quality of the signal allowed scientists to 'hear' the newly formed black hole ringing like a bell and measure three separate vibrational tones for the first time - all of which matched the predictions of Einstein's general theory of relativity exactly.
This represents the most precise test of general relativity ever conducted using gravitational waves and provided independent confirmation of Stephen Hawking's black hole area theorem.
Two signals detected just a month apart - GW241011 in October 2024 and GW241110 in November 2024 - suggest that the black holes involved may themselves be the result of earlier mergers. These 'second generation' black holes are thought to form in extremely dense regions of space, such as stellar clusters, where black holes can collide repeatedly.
The unusual spin characteristics of the objects in both events are what point scientists toward this conclusion. As the catalogue grows, researchers are now beginning to map distinct populations and life histories of black holes across the Universe.
The growing catalogue has also enabled a new, independent measurement of the Hubble constant - the rate at which the Universe is expanding. The new estimate from GWTC-5 is around 25 per cent more precise than the previous gravitational wave measurement.
Researchers were also able to test whether gravity behaves as Einstein predicted on the largest scales of the universe - something in question, given the mysterious cosmological component known as dark energy. The data in this release indicate that Einstein's theory of General Relativity does hold for the universe.
The updated catalogue of all gravitational wave events observed to date has been published with corresponding scientific papers in submission to Astrophysical Journal and Astrophysical Journal Letters.
Institute of Cosmology and Gravitation
As a recognised international centre of research excellence, the University of Portsmouth's Institute of Cosmology and Gravitation (ICG) brings together more than 70 researchers - faculty, postdoctoral fellows and PhD students - tackling some of the Universe's most profound mysteries, from the earliest moments after the Big Bang to the large-scale structure of galaxies, dark energy and gravitational waves.
The institute's contributions include roles in major international projects such as the Dark Energy Spectroscopic Instrument (DESI) , Euclid , LISA (Laser Interferometer Space Antenna) , and the LIGO gravitational wave detectors .
