Researchers from the University of Glasgow’s Institute for Gravitational Research are celebrating the publication of a vast new treasure trove of gravitational wave detections, hailed as a milestone marking the coming of age of gravitational astronomy.
The Gravitational Wave Transient Catalogue-5.0, or GWTC-5, is released online, with corresponding scientific papers submitted to Astrophysical Journal and Astrophysical Journal Letters.
This latest update details a total of 161 new signals from colliding black holes detected between April 2024 and the end of January 2025 by the gravitational wave detectors LIGO in the United States, Virgo in Italy, and KAGRA in Japan, known as the LVK collaboration. The publication brings the total number of gravitational wave signals detected to date to 390.
The most significant findings detailed in this collection include evidence for the existence of second-generation black holes, the most precise sky localization ever achieved for a gravitational wave source, and the first measurement of three vibrational modes of a black hole.
Astrophysicists at the University of Glasgow have played key roles in gravitational wave research since the 1970s. They led on the development of the delicate mirror suspensions at the heart of the US National Science Foundation Laser Interferometer Gravitational-wave Observatory (NSF LIGO) detectors, which make the detections possible.
Since the historic first direct detection in September 2015, they have worked closely with colleagues across the international LVK collaboration to improve the performance of the detectors and the data analysis of the detections, which are becoming more frequent as the detectors become more sensitive.
During observing runs, the collaboration’s detectors have picked up between three and four signals each week, with more frequent detections expected in future observing runs.
The collaboration alternates periods of data collection called observing runs with phases devoted to detector upgrades and commissioning. That’s also why the gravitational wave event catalog, including validated data and the physical parameters of the sources, is updated and shared with the wider scientific community approximately every six months.
Dr. Daniel Williams, a research fellow at the Institute for Gravitational Research, is co-chair of the LSC’s Compact Binary Science Working Group. He said, “This bumper update has once again broadened and deepened our knowledge of the universe, and given us many more glimpses of its most elusive objects: colliding black holes.
Sharper signals and historic clarity
“Just ten years ago, we made the first detection of gravitational waves from one of these events, and it’s a real testament to the work of hundreds of scientists around the world that we’re now detecting and analyzing hundreds of them.
“At Glasgow we’ve been at the forefront of developing new technology to make the detectors more sensitive, allowing us to see more of these signals, more clearly, and from collisions much further away than we could a decade ago. We also lead the development of critical analyses that allow us to extract so much information from each signal: decoding the properties of black holes colliding billions of light years away from Earth, all from a measurement which shifts our detectors by a fraction of the size of an atomic nucleus.”
In addition to the new perspectives opened by this extraordinary number of observations, the new catalog also includes several detections that are themselves exceptional and set new records in gravitational-wave astronomy observations: the best sky localization ever achieved for a gravitational wave source, the clearest gravitational wave signal ever recorded, and evidence for the existence of second-generation black holes.
A signal detected by the two LIGO detectors in the United States and Virgo in Italy on June 15, 2024—and therefore called GW240615—set the record for the most precise sky localization among all gravitational wave events observed to date. The source was identified within an area of just 6 square degrees, a relatively small portion of the celestial sphere.
The gravitational wave event observed with this record localization was the merger of two black holes, with masses of about 26 and 30 solar masses, which violently collided more than 3 billion light-years from Earth.
Using waves to measure expansion
Alex Papadopoulos, a postgraduate researcher at the Institute for Gravitational Research, said, “The updated GWTC-5.0 catalog gives us a much larger collection of gravitational-wave signals to help answer one of the biggest questions in cosmology: how fast is the universe expanding?
“The rate of this expansion is described by a value called the Hubble constant. Gravitational waves allow us to measure this by estimating how far away merging objects are, either directly from the signal itself or by identifying the galaxy where the merger took place.
“One of the major improvements in GWTC-5.0 compared to previous catalogs is the inclusion of observations from the Virgo detector, which returned after not participating in the previous observing run. With this additional detector, we can pinpoint the location of gravitational-wave signals on the sky much more accurately, making it easier to identify the host galaxy of each merger. Our expanded library of detections also meant we could use 236 signals, almost double the previous number, in our analyses. Each event contributes a small amount of information, so together these additional signals significantly improve our results.
“Together, these improvements help us measure the Hubble constant more precisely than ever before using gravitational waves, bringing us closer to understanding one of modern physics’ most important open questions.
“In Glasgow, we developed and tested software that allows this analysis to run more than a thousand times faster than before, even with the growing number of gravitational-wave signals in the catalog. This speed-up meant we could test many more possible scenarios and check that our results were as robust and reliable as possible, with the coordination of this effort led by our Institute for Gravitational Research.”
The clearest signal ever recorded
Detecting gravitational waves does not simply mean capturing a signal, but extracting it from the noise that disturbs the detectors. This requires highly sophisticated data analyses, which is why the “strength” or “clarity” of a signal is expressed through the signal-to-noise ratio (SNR). The catalog published today includes the “clearest” gravitational wave signal ever detected, with a signal-to-noise ratio of 76.9.
This signal, GW250114, reached Earth on January 14, 2025 and was generated by the merger of two black holes with nearly identical masses (32 and 34 times the mass of the sun, respectively), occurring more than one billion light-years from Earth. Its “clarity” made it possible to achieve some outstanding scientific results, among them the most accurate test of general relativity ever performed and confirmation of Stephen Hawking’s black hole area theorem.
Dr. John Veitch, an academic at the University of Glasgow who analyzes black hole signals, said, “With the loudness of GW250114 we are able to compare the warped space-time before and after the black holes merged, and found that the total area of the event horizons (the surface of ‘no-return’) increased in accordance with Hawking’s laws of black hole mechanics.
“After the merger, the final black hole rings like a bell, giving off gravitational waves instead of sound. Analyzing these waves confirmed that although energy is given off in gravitational waves during the merger, the total entropy of the black holes increases in accordance with the second law of thermodynamics. This shows that even for black holes the laws of thermodynamics still apply, but unlike normal objects, the more energy they hold, the colder they become.”
Clues to second-generation black holes
In October and November 2024, just one month apart, two additional very special black hole mergers were detected: GW241011 and GW241110, occurring approximately 700 million and 2.4 billion light-years from Earth, respectively.
Certain characteristics of these mergers—in particular the spin of the black holes (that is, the orientation and speed of their rotations)—indicate the objects involved could be “second-generation” black holes, meaning black holes that are themselves the result of previous coalescences. These objects likely formed in very dense and crowded cosmic environments, such as stellar clusters, where black holes are more likely to collide and merge repeatedly.
The growing number of observed events has also enabled researchers to study and increasingly clearly identify the properties of different populations of black holes, and one of the articles accompanying the catalog deals precisely with this specific aspect.
Building a population-wide picture
Storm Colloms, a postgraduate researcher at the Institute for Gravitational Research, said, “I’ve been part of the team understanding the processes that create merging black holes and neutron stars with the latest set of observations. We studied 267 sources, including 104 new observations. This set of hundreds of observations allows us to confidently measure the masses, spins and distances of binary black holes, and probe the correlations between these properties. In particular, we find that black holes with different mass ranges have different spins, indicating that there are distinct formation pathways that create unique groups of systems.
“This trend was hinted at by previously published observations, GW241011 and GW241110, pairs of black holes with clearly measured high spins and unequal masses. These two observations showed characteristic signs that the larger black hole in each pair was formed not directly from a massive star, but from a previous merger of two black holes. The signatures of black holes formed from previous mergers persist in the population as a whole, indicating that GW241011 and GW241110 are not one-of-a-kind, but trace an underlying trend. Now, we have growing evidence that there are ways that the universe creates merging black holes in addition to those that come from massive binary stars.
“The latest measurements of the population of gravitational wave sources continue to bring us closer to painting a clear picture of the origins of binary black holes and neutron stars. With upcoming observing runs and more sensitive detectors, we will get more precise measurements of individual sources and increase the number of sources in our catalogs, allowing us to probe more and more detailed astrophysics of compact object formation.”
Dr. Williams added, “We’re now detecting so many of these signals that we’re not just learning about individual collisions; it’s the astronomical equivalent of uncovering an ancient civilization. Today’s new results are like finding a previously undiscovered hoard, revealing not just individual lives, but the structure of an entire lost world.”
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Astrophysicists strike black gold with treasure trove of gravitational wave detections (2026, May 26)
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