A decade ago, detecting a single ripple in spacetime was a Nobel Prize-winning event that made headlines around the world. Now scientists are logging them several times a week. The LIGO-Virgo-KAGRA collaboration has released the largest gravitational wave catalog ever assembled, adding 161 new black hole collisions and pushing the all-time total to 390.
The release, known as GWTC-5.0, does more than pad a list. It marks the moment gravitational wave astronomy stopped being a series of one-off triumphs and became a mature, statistical science – one that can now study black holes by the hundred rather than one at a time.
From One Signal in 2015 to Several a Week
The first direct detection of a gravitational wave came in 2015, when instruments picked up the faint tremor of two black holes merging more than a billion light-years away. It confirmed a century-old prediction by Einstein and opened an entirely new way of observing the universe – by listening to the vibrations of spacetime itself rather than collecting light.
What has changed since is sensitivity. The detectors have been upgraded to the point where they now register three to four signals every week, according to the collaboration’s announcement. A phenomenon that was once vanishingly rare is now, in effect, a steady stream of data.
How the Detectors Hear a Ripple
Detecting a gravitational wave is one of the most delicate measurements in all of science. Each observatory is a giant L-shaped ruler, its arms kilometres long, with laser light bouncing between mirrors at either end. When a wave rolls through, it stretches one arm and squeezes the other by a fraction of the width of a proton – a distortion thousands of times smaller than an atomic nucleus. Sensing something that faint means filtering out everything from distant earthquakes to passing lorries.
What made the latest run so productive was a string of upgrades to that machinery. Better mirror coatings, more powerful and more stable lasers, and a quantum trick known as light squeezing all combined to push the detectors’ reach further into space. The further they can hear, the larger the volume of the universe they survey – and the more collisions fall within earshot each week.
That precision is also why the collaboration is so careful about false alarms. Every candidate signal is checked against the detectors that were online at the time, and against detailed models of what a real merger should look like, before it earns a place in the catalog. The 161 new entries are the survivors of that vetting – not raw blips, but events the team is confident were genuine cosmic collisions.
161 New Collisions in a Single Run
The bulk of the new catalog comes from a single stretch of observing. Combining two segments of the fourth observing run, from April 2024 to the end of January 2025, the instruments recorded 161 fresh detections. Remarkably, that one run accounts for roughly 75% of every gravitational wave ever detected since 2015 – a striking illustration of how much faster discovery now moves.
Three widely separated instruments made it possible: the two LIGO detectors in the United States, Virgo in Italy and KAGRA in Japan. Working together, they can not only sense a passing wave but triangulate roughly where in the sky it came from, turning a whisper into a location.
The haul came from the observing campaign known as O4, split across two stretches of data-taking between 2024 and early 2025. Because the instruments were more sensitive than in any previous run, they did not just detect more events – they detected them further away, sampling collisions that happened billions of years ago when the universe was younger and denser. Each new entry in the catalog is another data point in a rapidly filling map of cosmic history.
Black Holes Built From Black Holes
Among the most intriguing findings is growing evidence for what astronomers call hierarchical mergers – black holes that appear to be the products of earlier black hole collisions. The catalog includes two events that may be exactly that: black holes assembled from the remnants of previous mergers, rather than formed directly from a collapsing star.
That matters because it hints at where these objects live. Building a black hole out of smaller black holes requires a crowded environment, such as a dense star cluster, where merged objects can find new partners and merge again. Each such event is a clue to the cosmic neighbourhoods that manufacture the universe’s heaviest objects.
Hearing a Black Hole ‘Ring’
The catalog also contains the clearest gravitational wave signal ever recorded, and with it a rare feat: the first measurement of three distinct vibrational modes of a black hole. When two black holes merge, the newborn object ‘rings’ like a struck bell before settling down, and the exact tones of that ringing are dictated by the laws of gravity.
Measuring several of those tones at once is a stringent test of Einstein’s general relativity and of predictions about black holes that trace back to Stephen Hawking. So far, the results line up with theory – a quiet but profound confirmation that our understanding of gravity holds even in the most extreme conditions the universe can produce.
Why This Turns Discovery Into Statistics
The real power of a catalog this size is statistical. With a handful of events, every detection is an anecdote; with hundreds, scientists can start to map the whole population – how massive these black holes tend to be, how fast they spin, how often they collide and how that has changed over cosmic time. That population view is where the deepest questions get answered.
Early looks at the population are already turning up structure. The masses of these black holes are not spread evenly but seem to cluster at particular values, hinting at the specific ways massive stars live and die. Their spins, and how those spins are tilted, carry clues about whether a pair was born together from two sibling stars or met by chance in a crowded cluster. None of these patterns is visible in a single event; they emerge only once you have hundreds to compare. It is the difference between meeting one person and taking a census of an entire city.
Handling that flood of data is its own challenge, and sifting genuine signals from detector noise increasingly leans on machine learning, part of the broader surge in AI capability we covered in our look at OpenAI’s new model family. The instruments may be listening to the cosmos, but modern software is doing much of the hearing.
What Comes Next
The trajectory points in one direction: more. Future observing runs and further upgrades will push sensitivity higher still, extending the reach of the detectors deeper into the universe and further back in time. Planned next-generation observatories promise to turn today’s weekly cadence into a near-continuous census of merging black holes and neutron stars.
Neutron stars are a particular prize. When two of them collide they can throw off a visible burst of light and forge heavy elements such as gold and platinum, so catching more of these mergers would tie the ripples in spacetime directly to the origin of the material world. The bigger the catalog grows, the better the odds of capturing another such event close enough to study in fine detail.
There is also the tantalising prospect of hearing events alongside seeing them – catching the light from a cosmic collision at the same moment its gravitational waves arrive, a technique that has already begun to rewrite parts of astrophysics. For now, GWTC-5.0 stands as a milestone: proof that a field which began with a single, hard-won signal has grown into one of the most productive corners of modern science, quietly reshaping how we listen to the universe.
