The collaborating gravitational-wave detectors around the world—LIGO, Virgo, and Kagra—have added 161 new detections to their catalog of scientific results.
The detections date from the period April 2024 to January 2025. During that period, the European Virgo detector in Pisa was also back in operation after a long period of maintenance and upgrades. Nikhef is closely involved with Virgo and participates in the analysis of the measurements by the LVK collaboration.
The entire LVK catalog of gravitational waves now comprises 390 signals since the first observation in 2015. The new catalog was submitted today to the journal Astrophysical Journal.
The expanding collection has recorded a number of remarkable events, and increasingly enables statistical studies of black hole populations. LVK currently detects three to four gravitational waves per week.
Gravitational waves are ripples in space and time caused by extremely violent events in the universe, such as black hole collisions. Black holes warp space so that no light can escape. When two black holes collide, this leads to an abrupt change in spacetime, which propagates as an observable wave.
Gravitational waves are measured using laser interferometers, which can measure distances between mirrors with extreme precision. The arms of the two LIGO detectors are 4 kilometers long, and those of Virgo are 3 kilometers long. At these distances, gravitational waves cause length changes smaller than the diameter of a hydrogen atom, but they can still be measured using special techniques.
The catalog contains several interesting observations. Among them is an event on June 15, 2024, that was detected by the two LIGO detectors and Virgo. By combining the measurements, the source of the wave in the sky could be pinpointed with record precision: an area of 6 square degrees, more than five times the size of the full moon.
Thanks to the improved localization, better estimates can also be made of the expansion rate of the universe itself, the so-called Hubble constant. The value found corresponds with existing astronomical measurements, but does not yet help to clarify persistent discrepancies between existing measurements.
On January 14, 2025, the most powerful gravitational wave signal ever observed was detected: 76.9 times stronger than the background noise. That signal was used to succesfully test a prediction by Stephen Hawking regarding the size of black holes.
In October and November 2024, two signals were detected, originating from collisions between extremely rapidly rotating black holes. It is suspected that these black holes themselves were formed earlier in collisions between black holes, resulting in the new black holes rotating very rapidly.
Most results have been published seperately already, but together they show how crucial detector upgrades are for increasing sensitivity, said gravitational wave expert Chris Van Den Broeck of Nikhef and Utrecht University.
