Two black hole collisions detected in late 2024 have provided unprecedented tests of Einstein's general theory of relativity. The events, captured by the LIGO-Virgo-KAGRA Collaboration, revealed unusual spins and possible second-generation black holes. These detections confirm theoretical predictions with high precision and probe for new particles.
In late 2024, the LIGO-Virgo-KAGRA Collaboration detected two remarkable gravitational wave signals from black hole mergers, announced in a study published on October 28, 2025, in The Astrophysical Journal Letters. The first event, GW241011, occurred on October 11, 2024, approximately 700 million light-years from Earth. It involved the merger of black holes with masses of about 20 and 6 times that of the Sun, with the larger one identified as one of the fastest-spinning black holes ever observed.
Roughly a month later, on November 10, 2024, the second event, GW241110, was detected 2.4 billion light-years away. This merger featured black holes of roughly 17 and 8 solar masses, where the main black hole spun in the opposite direction to its orbit—the first such observation.
"Each new detection provides important insights about the universe, reminding us that each observed merger is both an astrophysical discovery but also an invaluable laboratory for probing the fundamental laws of physics," said co-author Carl-Johan Haster, assistant professor of astrophysics at the University of Nevada, Las Vegas. "Binaries like these had been predicted given earlier observations, but this is the first direct evidence for their existence."
These events occurred during the fourth observation campaign (O4) of the LIGO-Virgo-KAGRA network, which began in May 2023 and continues through mid-November 2025. To date, about 300 black hole mergers have been detected. Both GW241011 and GW241110 suggest second-generation black holes formed through hierarchical mergers in dense environments like star clusters, with significant mass differences and unusual spins.
"GW241011 and GW241110 are among the most novel events among the several hundred that the LIGO-Virgo-KAGRA network has observed," said Stephen Fairhurst, professor at Cardiff University and spokesperson for the LIGO Scientific Collaboration. "With both events having one black hole that is both significantly more massive than the other and rapidly spinning, they provide tantalizing evidence that these black holes were formed from previous black hole mergers."
The precision of GW241011's detection allowed tests of Einstein's general relativity in extreme conditions, matching predictions from his equations and Roy Kerr's rotating black hole model with record accuracy. A rare "higher harmonic" in the signal provided another confirmation. These mergers also rule out certain masses for ultralight bosons, hypothetical particles beyond the Standard Model.
"These two binary black hole mergers offer us some of the most exciting insights yet about the earlier lives of black holes," said Thomas Callister, co-author and assistant professor at Williams College. "They teach us that some black holes exist not just as isolated partners but likely as members of a dense and dynamic crowd."
Upgrades to the detectors will enable further studies of such systems, enhancing understanding of black hole formation and fundamental physics.