The newly published Gravitational Wave Transient Catalogue-5.0 (GWTC-5) has been released online, with companion research papers submitted to Astrophysical Journal and Astrophysical Journal Letters.

The latest catalog adds 161 newly identified signals from colliding black holes detected between April 2024 and the end of January 2025 by the LIGO detectors in the United States, Virgo in Italy, and KAGRA in Japan. Together, these facilities make up the international LVK collaboration. With these additions, the total number of confirmed gravitational wave detections has now reached 390.

The expanded catalog includes several landmark discoveries. Among them are new evidence for second-generation black holes, the most accurate sky localization ever achieved for a gravitational wave source, and the first measurement of three vibrational modes from a black hole.

Decades of Work Behind the Discoveries

Researchers at the University of Glasgow have been involved in gravitational wave science since the 1970s. Their team played a leading role in designing the ultra sensitive mirror suspension systems used in the US National Science Foundation Laser Interferometer Gravitational-wave Observatory (NSF LIGO), technology that is essential for detecting the tiny distortions in space-time caused by gravitational waves.

Since the first direct detection of gravitational waves in September 2015, Glasgow researchers have continued working alongside scientists across the LVK collaboration to improve both detector performance and data analysis techniques. As the instruments have become increasingly sensitive, the number of discoveries has continued to grow.

During observing runs, the network is now detecting roughly three to four gravitational wave events every week. Scientists expect that rate to rise further as future upgrades improve detector sensitivity.

The collaboration alternates between observing runs that collect scientific data and periods dedicated to commissioning and upgrading the detectors. Because of this cycle, the validated gravitational wave catalog, including source properties and other measurements, is typically updated and shared with the scientific community about 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.

"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."

Record Breaking Gravitational Wave Discoveries

Beyond dramatically increasing the number of known gravitational wave events, GWTC-5 includes several observations that have set entirely new records for the field.

Among the highlights are the most precisely located gravitational wave source ever observed, the clearest gravitational wave signal ever recorded, and additional evidence supporting the existence of second-generation black holes.

One particularly important event, known as GW240615, was detected by the two LIGO observatories in the United States together with Virgo in Italy on June 15, 2024. This observation achieved the most accurate sky localization of any gravitational wave source to date.

Scientists narrowed its origin to an area covering only six square degrees, a remarkably small region of the sky. The event was produced when two black holes with masses of approximately 26 and 30 times that of the Sun merged more than three billion light-years from Earth.

Measuring the Expansion of the Universe

Alex Papadopoulos, a postgraduate researcher at the Institute for Gravitational Research, explained that the expanded catalog is also helping scientists tackle one of cosmology's biggest unanswered questions: how fast the Universe is expanding.

He said:

"The updated GWTC-5.0 catalogue 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 catalogues 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 catalogue. 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 Gravitational Wave Signal Ever Detected

Finding a gravitational wave involves much more than simply recording a signal. Scientists must separate the faint ripple in space-time from the background noise constantly present in the detectors. That process requires sophisticated data analysis, which is why researchers describe a signal's strength using its signal-to-noise ratio (SNR).

Among the events in the new catalog is the clearest gravitational wave ever observed. The signal achieved an SNR of 76.9, making it the strongest detection on record.

Known as GW250114, the signal reached Earth on January 14, 2025. It was produced by the merger of two black holes with very similar masses (32 and 34 times the mass of the Sun, respectively) more than one billion light-years away.

Because the signal was exceptionally clear, researchers were able to perform some of the most detailed tests ever conducted using gravitational waves. These included the most precise test of general relativity to date 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."

Evidence for Second-Generation Black Holes

The catalog also highlights two unusual black hole mergers detected just one month apart during late 2024.

The first event, GW241011, occurred roughly 700 million light-years from Earth. The second, GW241110, took place about 2.4 billion light-years away.

Researchers found that the spins of the black holes (that is, the orientation and speed of their rotations) suggest these objects may be second-generation black holes. Instead of forming directly from collapsing stars, these black holes may have already been created by earlier black hole mergers before colliding again.

Scientists believe repeated mergers like these are most likely to happen in crowded environments such as dense stellar clusters, where black holes have many opportunities to interact and eventually collide.

Building a Census of Black Hole Populations

As the number of gravitational wave detections continues to grow, researchers can move beyond studying individual events and begin examining the broader population of black holes throughout the Universe.

One of the scientific papers accompanying GWTC-5 focuses specifically on identifying patterns among hundreds of black hole systems and what those patterns reveal about how these objects form.

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 continues 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 catalogues, allowing us to probe more and more detailed astrophysics of compact object formation."

A New Era for Gravitational Wave Astronomy

The rapid increase in gravitational wave detections is changing the way astronomers study the Universe. Instead of focusing on a handful of extraordinary events, researchers now have hundreds of observations they can compare, allowing them to uncover larger patterns in how black holes and other compact objects form and evolve.

According to Dr. Daniel Williams, the growing catalog represents a fundamental shift in what gravitational wave astronomy can achieve.

He said:

"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 civilisation. Today's new results are like finding a previously undiscovered hoard, revealing not just individual lives, but the structure of an entire lost world."

As gravitational wave observatories continue to improve, scientists expect the pace of discoveries to accelerate even further. More sensitive detectors will capture additional black hole and neutron star mergers, producing increasingly precise measurements and offering fresh insights into some of the Universe's most extreme objects.

The publication of GWTC-5 marks another milestone for the international gravitational wave community. Beyond adding 161 new detections to the scientific record, the catalog provides an unprecedented dataset that researchers can use to investigate black hole evolution, test the laws of physics under extreme conditions, and refine measurements of the expanding Universe.

The University of Glasgow's contributions to this work were supported by funding from UKRI's Science and Technology Facilities Council (STFC). Other UK gravitational wave research groups receiving STFC support include the Universities of Birmingham, Cambridge, Cardiff, Kings College London, Nottingham, Portsmouth, Sheffield, Strathclyde, University College London, Queen Mary University, and the University of the West of Scotland.