Scientists analyzing gravitational-wave data from LIGO–Virgo–KAGRA have found evidence that giant black holes may form through repeated mergers in dense star clusters, rather than a single collapse. The study, led by Cardiff University researchers, analyzed data from 153 black hole mergers and found a clear split between two types of black holes, with the heavier ones likely formed through multiple mergers.

The research suggests that these heavy black holes may not have formed directly from stars, but rather through earlier black hole mergers, built up step by step inside dense clusters where interactions are frequent.

The study's findings challenge long-standing models of stellar evolution and add a new layer to the understanding of black hole growth. The data shows that black holes near and above roughly 45 times the mass of the Sun are sitting in or close to the so-called “mass gap”, where objects should not exist if they formed directly from collapsing stars.

The researchers believe that this phenomenon may give clues on the peculiarities of supermassive black holes detected by gravitational waves, since their patterns of spins and masses clearly suggest multiple collisions rather than the creation of one.

The study's lead author says that the findings have significant implications for black hole research, suggesting that black holes may not just be the final stage of a dying star, but rather part of a much longer chain of cosmic evolution inside star clusters. The court will resume hearing on the implications of this study on Tuesday.