The Fourth Update to the Gravitational-Wave Transient Catalogue
Alongside the release of the O4a data on the 26th of August 2025, the LIGO–Virgo–KARGA (LVK) Collaboration published the latest update to the Gravitational-Wave Transient Catalogue (GWTC), bringing the version from 3.0 to 4.0. This update added 128 probable gravitational-wave signals, more than doubling the number observed by the LVK.
Within the 128 new additions came some LVK record-breakers: from likely the most massive binary system observed, GW231123_135430, to the loudest (signal-to-noise ratio of ~40) detection, GW230814_230901 (since beaten, but still very good). Also included were two candidates thought to be from neutron star-black hole binaries, GW230529_181500 and GW230518_125908, the latter detected during the pre-O4 engineering run. Perhaps the most exciting news for the Gravity Spy project is that of the 128 events, 37 required glitch mitigation, that’s almost 30%! In the case of GW230708_053705 we have a great example of a glitch overlapping in time with a gravitational-wave signal in the Hanford detector.
Following the release of GWTC-4.0, the LVK published papers covering topics such as tests of Einstein’s theory of gravity, known as general relativity, and implications for cosmology, showcasing the science that can be performed with gravitational wave data.
We have lots to look forwards to in future updates to the GWTC as there are many results from O4b, planned to be released in under two weeks, and O4c still to come.
Happy classifying 🕵️♀️,
Elizabeth
For more information about the data release, take a look at this LIGO news article and this recent LVK webinar.
That’s a Wrap: The End of O4
At 16:00 UTC on the 18th of November, the fourth observing period (O4) of the LIGO–Virgo–KAGRA (LVK) Collaboration came to an end. Starting in May 2023, the LVK’s longest observing run yielded over 250 gravitational-wave candidates. Highlights published so far include the most massive merger seen to date, GW231123, a pair of events showing evidence of unusual and high black hole spins, GW241011 and GW241110 and a merger between a neutron star and a small black hole, GW230529. Upgrades performed before O4 brought the LVK detectors to their highest sensitivity yet, increasing the rate of gravitational-wave detection and allowing O4 to detect more than double the number of the three previous observation runs. O4 also saw the first time the four LIGO, Virgo and KAGRA detectors were observing simultaneously, marking a key milestone in gravitational-wave international collaboration!
The LVK detected over 250 gravitational-wave candidates during O4, more than double the amount detected during the previous observing runs. Image courtesy of the LIGO-Virgo-KAGRA Collaboration.
Recently, the LVK released the data collected during the first period of O4 (O4a) in the fourth update to the Gravitational Wave Transient Catalogue (GWTC) and we can look forward to future updates covering the second and third period (O4b and c) in May and December 2026.
When the LVK detectors will next be observing is currently uncertain, with an as-of-yet unnamed 6-month observing run set to take place sometime in the northern hemisphere summer/autumn of 2026, before we take a longer break as the detectors are upgraded in time to begin O5 in 2028, although this start date is currently being reassessed. The LVK keep their observing plan page updated with latest decisions.
For now, keep an eye out for glitches from the last parts of O4c’s data, which will be uploaded to Gravity Spy soon!
Happy classifying 🕵️♀️,
Elizabeth
Gravity Spy 