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These events are gravitational waves, ripples in spacetime produced when two extremely massive objects, such as black holes, collide. These waves propagate through the Universe and can be detected on Earth using extremely sensitive instruments. The LIGO, Virgo, and KAGRA observatories work together to capture these faint signals.
When two black holes collide and merge, they release gravitational waves. These waves are detected by the LIGO-Virgo-KAGRA observatories on Earth, allowing scientists to determine the mass and spin of the black holes.
Credit: Maggie Chiang for Simons Foundation
Since the first detection in 2015, the number of observations has continued to grow. With this new catalog, scientists are reaching a significant milestone. In just a few months of observation, they recorded more signals than in all previous observing runs combined.
This accumulation is changing the way astronomy is done. Researchers are no longer limited to studying isolated cases. They can now analyze entire populations of black holes and compare their properties, such as their mass or spin rate.
Among the notable discoveries is an exceptional collision between two black holes, each about 130 times the mass of the Sun. This is much larger than the majority of systems observed so far, which are typically around 30 solar masses. Such a mass indicates that these objects are themselves the result of previous collisions.
Other signals also stand out. Some show black holes spinning at dizzying speeds, close to half the speed of light. Others reveal highly unbalanced systems, where one object is much more massive than its partner.
The LIGO project operates two detection sites: one near Hanford in Washington State, and another near Livingston in Louisiana.
Credit: LIGO Collaboration
These observations provide a better understanding of how black holes form. They indicate that some are born in very dense environments where successive collisions are possible. The Universe thus appears as a dynamic place, in perpetual transformation.
Gravitational waves also offer a unique way to test Einstein's theory of general relativity. This theory describes gravity as a curvature of space and time. Black hole collisions, among the most extreme phenomena known, provide an ideal testing ground to verify if its predictions always hold true.
So far, the results confirm the robustness of this theory. The observed signals match its predictions very precisely. But scientists continue to search for potential anomalies that could reveal new physical laws.
Finally, this data allows tackling another major question: the expansion rate of the Universe. By analyzing gravitational waves, it is possible to directly estimate the distance to the sources. This offers an independent method for calculating the Hubble constant, a key parameter in cosmology.
Initial estimates from this catalog indicate an expansion rate of about 47 miles per second per megaparsec (approximately 76 kilometers per second per megaparsec). Even though this measurement still needs refinement, it helps enrich an ongoing scientific debate.
With these new observations, gravitational wave detectors are gradually transforming our view of the cosmos. What was once invisible becomes measurable, paving the way for an ever more precise exploration of the Universe.