Earlier in the year I wrote a post which tried to answer the apparently simple question “how many gravitational waves have we detected?”. Well, with today’s announcement of 128 new detections, it’s time to update my calculations.
The same caveat as before: I’m writing this as a blog post and a simple note, and the numbers here haven’t been reviewed, and certainly haven’t been endorsed by the LIGO Scientific Collaboration, or indeed anyone else in any official position. I’ve also not included any information beyond what’s public. You’ll need to wait a bit longer for that!
Published by the LIGO-Virgo-KAGRA Collaborations (O1-O4a)
The normal number used in papers for the number detected thus far is the one derived from GWTC-4.0, the LVK’s flagship results paper which covers the first three observing runs, and the first part of the fourth.
That contains 209 binary black hole (BBH) signals, 7 neutron star black hole (NSBH) signals, and 2 binary neutron star (BNS) signals, for a total of 218 events. However there are two additional signals which are a bit ambiguous. One of them just misses out on the significance criteria for the catalogue (GW200105_162426, which is one of the NSBH events in O3b), and GW230630, which we think is most likely to be of instrumental origin.
So the headline here:
The LVK has published 218 confident gravitational wave detections in the first three observing runs, plus the first part of the fourth observing run.
A breakdown of where these first appeared is in the table below.
| Observing run | Catalogue update | BBH | NSBH | BNS |
|---|---|---|---|---|
| O1 | GWTC-1.0 | 3 | 0 | 0 |
| O2 | GWTC-1.0 | 7 | 0 | 1 |
| O3a | GWTC-2.1 [1] | 42 | 2 [2] | 1 |
| O3b | GWTC-3.0 | 31 | 4 [3] | 0 |
| O4a | GWTC-4.0 | 126 | 2 | 0 |
Published by other authors
Gravitational-wave detector data is eventually made publicly available, so anyone is able to search for signals in it. And they have.
In January 2025 I put together a paper which reviews all of the events claimed in the literature.
In summary there are 61 further events claimed across the literature. I was able to reproduce results for 57 of these. There are some notes in my paper about how some of these “community” events have been received, but if they’re all taken as being real:
In total 279 events have been claimed across the literature.
This would extend to 280 events if GW200105_162426 is included.
I expect there’s a high probability that this number will increase as more machine learning algorithms are applied, and more exotic regions of parameter space are explored by search algorithms on archival data.
So, for the first three observing runs (2015-2020) there are between 90 and 152 claimed events, depending on how you wish to select events.
Public announcements by the LVK in O4
We can now go deeper into the realms of speculation, and look at the number of publicly announced triggers in O4 from the collaborations.
In O3b, there were 105 further alerts which have not been retracted. Then in the ongoing O4c (correct as of 2025-08-26) there have been a further 39.
The LVK have issued alerts for 224 events in O4, 144 of which are not contained elsewhere in the literature.
The LVK has announced 362 gravitational-wave signals; 218 have been published as confident detections, 144 more have only been issued as alerts.
So, In total 423 gravitational-wave signals have been claimed across the literature, though not all are published or claimed as detections.
So what’s the answer?
The “official” LVK answer is 218 events, which is also the smallest possible number. The largest, but most unreliable, is 423, since it’s made by including lots of alerts which may not end-up being claimed as detections.
Footnotes
- GWTC-2.1 should be considered the definitive list of events from O3a, and provides an update relative to GWTC-2, having used the final calibration of the strain data and improved denoising techniques which were later used for GWTC-3. GWTC-2.1 presented 8 additional BBH events compared to GWTC-2.
- I have included GW190814 in the list of NSBH events, but the precise nature of the lower mass object (the “grey hole”) is unclear. GW190426_152155 fits more comfortably into the range for an NSBH event, however.
- A total of four events in O3b could be NSBH events; the fourth event is GW200105162426, which has p astro=0.36, but stands as a clear outlier from the noise distribution, so is not strictly contained within the 90 events which are generally claimed.