An international team of astronomers, including Australian researchers from the ARC Centre of Excellence for the Discovery of Gravitational Waves (OzGrav) at the Australian National University (ANU), detected two extraordinary black-hole mergers — GW241011 and GW241110 — using the LIGO, Virgo and KAGRA detectors.
These discoveries offer new clues about the formation and evolution of black holes and enable tests of Einstein’s general theory of relativity, since both events involve black holes of unequal masses and extremely rapid spins, possibly the result of previous mergers.
The two detections occurred in late 2024, only about a month apart, during the O4b observing phase of the global network of detectors. Each event was triggered by the violent collision of two black holes, creating an even more massive object and emitting ripples in spacetime that traveled hundreds of millions, or even billions, of years to reach Earth.
Both systems involved black holes with unequal masses and very rapid spins — a rare combination that offers a window into the processes that shape their origin and evolution, in addition to allowing exploration of new physics. Based on these signals, researchers from ANU and OzGrav studied the hypothesis that the rotation of black holes could reveal clues about still-unknown particles.
PhD student Aswathi Pampurayath Subhash, from ANU, led the analysis focused on ultralight bosons — hypothetical particles that could constitute dark matter. Some theories suggest that these particles gradually drain rotational energy from black holes.
However, as the observed black holes maintained rapid spins at the moment of merger, the scientists were able to rule out a wide range of possible masses for these bosons, thus constraining dark-matter theories.
“Rapidly spinning black holes, like those observed in GW241011 and GW241110, are more than astrophysical curiosities — they are tools for testing the existence of new particles,” explains Subhash.
“The fact that they maintain a high spin over their lifetimes allows us to exclude a wide range of possible masses for ultralight bosons, thereby setting new limits on dark matter and on theories beyond the Standard Model,” she adds.
The data also reveal details about the growth and evolution of black holes. Both mergers involved a black hole with twice the mass of the other, and in both cases the spins were tilted relative to the orbital plane — a feature that suggests these systems did not form from binary stars, but rather from successive hierarchical mergers in dense stellar clusters.
“These two mergers give us a remarkable view of how black holes grow and evolve,” says Ling (Lilli) Sun, OzGrav’s principal investigator and a professor at ANU.
“Their rapid spins and unequal masses indicate that they may be second-generation black holes — products of previous mergers in dense stellar environments. Each detection adds a new piece to the puzzle of how the universe’s most extreme objects form,” she adds.
The discoveries demonstrate the extraordinary sensitivity of the LIGO, Virgo and KAGRA detectors, which continue to unravel the hidden secrets of the cosmos.
“Each new detection not only deepens our understanding of black-hole formation, but also turns these cosmic collisions into true laboratories of fundamental physics,” concludes Professor Eric Thrane, OzGrav’s principal investigator at Monash University.
Together, the GW241011 and GW241110 detections mark another advance in gravitational-wave astronomy, revealing the hidden lives of merging black holes and bringing us closer to understanding the fundamental laws that govern the Universe.
