The new LIGO-Virgo-KAGRA catalog sets records in precision gravitational-wave astronomy

Researchers at the Max Planck Institute for Gravitational Physics contribute to discoveries in the largest gravitational-wave catalog ever compiled.

To the point

• New gravitational-wave catalog: The LIGO-Virgo-KAGRA collaboration releases the largest gravitational-wave catalog, GWTC-5, with 161 new events, totaling 390 confirmed detections since 2015.
• A wealth of results: The catalog contains many astrophysical highlights: the gravitational-wave source with the most precise sky localization, the first measurement of three gravitational-wave tones from a black hole, evidence for the existence of second-generation black holes, and new measurements of how fast the Universe is expanding.
• More results to come: Data from the last part of the fourth observing run are being analyzed at the moment. Information on the 68 signal candidates and new discoveries will be published in a catalog update in the coming months.

Today, the LIGO-Virgo-KAGRA (LVK) collaboration published an updated catalog of the gravitational-wave events observed by its international network of gravitational-wave detectors in the United States, Italy, and Japan. The new version of the catalog, called Gravitational-Wave Transient Catalogue-5.0 (GWTC-5), has been posted as three core and three companion papers on the arXiv preprint server. These will be submitted to The Astrophysical Journal and The Astrophysical Journal Letters.

The detector network collected the data analyzed in this work between April 2024 and the end of January 2025, during O4b, the second part the fourth joined observing run (O4). A total of 161 new gravitational-wave events were discovered, of which scientists extracted parameters from 104. The latest revision of the catalog increases the grand total of confirmed events observed by the network since the first detection in September 2015 to 390.

As detector upgrades make the instruments increasingly more sensitive, the number of events detected in each successive observing run is growing significantly. This is underlined by the fact that 75% of all gravitational-wave signals observed so far have been discovered in the first and second part of O4.

An ever-growing treasure trove of data

“Our detectors have now become so sensitive that we discover new gravitational-wave signals about three to four times each week of our observing runs, unlocking an ever-growing treasure trove of data,” says Frank Ohme, group leader in the Precision Interferometry and Fundamental Interactions department at the Max Planck Institute for Gravitational Physics (Albert Einstein Institute; AEI) in Hannover. “Each new signal helps to deepen our understanding of the dark, invisible side of the Universe.”

“Ten years after our first discoveries, we are now entering the era of precision gravitational-wave astronomy,” adds Karsten Danzmann, director emeritus at the AEI in Hannover. “What we can do with gravitational-wave astronomy today is truly amazing! We can study the population of coalescing black holes, conduct some of the most precise tests of general relativity, and obtain completely new measurements of the expansion of our Universe.”

“Our new catalog includes several exceptional and record-breaking signals,” says Alessandra Buonanno, director of the Astrophysical and Cosmological Relativity department at the AEI in the Potsdam Science Park. “We have found evidence for the existence of second-generation black holes, have pinpointed the sky position of a gravitational-wave source more precisely than ever before, and have for the first time measured or constrained three gravitational-wave tones from a black hole in the clearest gravitational-wave signal observed to date.”

“The collaboration did an extraordinarily careful and comprehensive analysis of the detected gravitational waves,” confirms Harald Pfeiffer, group leader at AEI in Potsdam and the lead reviewer for the internal quality control of data-taking and analysis of the GWTC-5.0 results paper. “This makes today’s announcements not only scientifically extraordinarily important, but also very reliable.”

Pinpointing a black hole coalescence

One signal in the catalog, observed on 15 June 2024, sets a new record for the most precise sky localization of all gravitational-wave events. Its source was found to lie within an area of just 6 square degrees – a patch of the sky that could be covered by about 28 full moons. This exceptional performance was possible because LVK researchers could combine data from both LIGO instruments and the Virgo detector, which observed the gravitational waves.

Determining where a gravitational-wave source is located is crucial when searching for possible electromagnetic signals generated by events such as binary neutron star or black-hole–neutron-star coalescences. The smaller the sky region, the easier it is to point other astronomical observatories at them.

The record-setting event came from the coalescence of two black holes, weighing 34 and 26 times as much as our Sun, respectively. The gravitational waves were emitted from their merger about 3.4 billion years ago – at a time when the earliest known forms of life emerged on Earth – and traveled at the speed of light until reaching our planet in 2024.

Data analysis expertise and new waveform models

Whenever gravitational-wave signals reached Earth, an international expert team reviewed the performance of the algorithms that identified the potential signals and also discussed the next analysis steps. AEI members contributed week-long shifts of data analysis expertise during the observing run.

Gravitational-wave astronomy goes far beyond simply detecting a signal’s presence. Using highly sophisticated data analyses, it must be extracted it from the detectors’ background noise and its astrophysical properties must be inferred and understood. The clearer a signal stands out from the noise background, the “louder” it is and the better its astrophysics can be understood.

Extracting astrophysical properties from these loud signals requires a detailed understanding of the characteristic fingerprints these properties leave in the data. For this purpose, researchers at the AEI in Potsdam and Hannover have developed and made key contributions to the latest generation of improved waveform models. LVK researchers use these models to predict the gravitational waves emitted from binary black holes and to understand new signals once found.

“Our improved waveform models are more physically consistent and accurate and are key to reliably infer the properties of black hole mergers from the detector data,” explains Héctor Estellés Estrella, a former postdoc at AEI Potsdam, now a Postdoctoral Fellow at the Institute of Space Sciences in Barcelona.

“The additional physics incorporated by us into existing waveform models, now used in GWTC-5, brings us a step closer to precisely modeling these complex astrophysical systems,” adds Shrobana Ghosh a postdoc in the Precision Interferometry and Fundamental Interactions department at AEI Hannover.

The clearest gravitational-wave signal

GWTC-5 contains five exceptionally loud binary black hole mergers including the by far clearest gravitational-wave signal seen to date. GW250114, reported earlier, came from a coalescence of black holes with masses 34 and 32 times that of our Sun about 1.3 billion light-years away. It was observed on 14 January 2025 and its “clarity” made it possible to achieve outstanding scientific results, among them the most precise test of general relativity ever performed and confirmation of Stephen Hawking’s black hole area theorem.

During the ringdown phase, when the black hole settles into its final state right after the merger, the gravitational-wave signal contains a characteristic spectrum of modes, or tones. Characterizing multiple gravitational-wave tones – measuring the frequencies of the tones and how quickly they fade – enables unique and powerful tests of general relativity. GW250114 was clear enough for the researchers to measure two tones and constrain a third. All three agree with Einstein’s general relativity and the Kerr solution for rotating black holes.

Characterizing black holes with DINGO

In the past years, researchers at the AEI and at the Max Planck Institute for Intelligent Systems (MPI-IS) have been developing DINGO, a machine learning algorithm for gravitational-wave data analysis. In the production of GWTC-5 it has been used routinely for the first time.

“Our approach called DINGO employs deep neural networks. It is just as accurate and reliable as the conventional methods the LVK collaboration uses to determine the astrophysical characteristics of the gravitational-wave sources, but it only takes minutes instead of hours or days for the same task,” explains Annalena Kofler, a PhD student at the MPI-IS and the AEI in Potsdam.

“The LVK investigated 104 of the 161 of the new gravitational-wave signals, in detail. For 42 of those 104 signals in the new catalog, DINGO served as a cross-validation tool. The DINGO results agree exactly with those obtained with the conventional methods,” adds Nihar Gupte, a PhD student in the Astrophysical and Cosmological Relativity department at the AEI in the Potsdam Science Park.

Second-generation black holes

In October and November 2024, just one month apart, the detector network observed gravitational waves from two very special black hole coalescences. GW241011 and GW241110 came from distances of approximately 700 million and 2.4 billion light-years, respectively.

As reported earlier, certain characteristics of these mergers – in particular how fast and around which axis the black holes were spinning – indicate the objects involved could be “second-generation” black holes. These are black holes that themselves were formed in previous black hole coalescences, likely in very dense and crowded cosmic environments, such as stellar clusters. There black holes are more likely to collide and merge repeatedly.

The growing number of observed events has also enabled the LVK researchers to study and identify the properties of different populations of black holes. One of the articles accompanying the catalog deals with this specific aspect.

Studying the expansion of our Universe

LVK researchers have used the improving ability of the detector network to localize events and the increased number of events to measure the rate at which our Universe is expanding. They combined gravitational-wave based measurements of the distances to the sources with other measurements of how fast they are traveling away from Earth because of the Universe’s expansion.

The LVK improved the precision of its estimate of the Hubble constant, which measures the Universe’s expansion rate, by more than 25% compared to the value derived from the previous catalog. The estimated value is consistent with existing measurements from both our cosmic neighborhood and the early Universe. It is, however, not yet precise enough to resolve the “Hubble Tension” between those long-established measurements.

More signals in the next catalog update and the upcoming observing run

The analysis of O4c, the final part of O4 from the end of January 2025 until mid November 2025, is currently underway. The LVK collaboration will publish the results in the coming months. The 68 signal candidates already identified during O4c will further expand the catalog and offer new opportunities to study our Universe and the fundamental laws of physics.

At the moment, the detectors of the international network are undergoing upgrades to improve their sensitivity towards the next six-month observing run, called IR1, beginning in late October or mid November of 2026. More sensitive instruments will help discovering gravitational-wave signals at an even higher rate – potentially uncovering additional rare cosmic events.