Scientists Discover Biggest Black Holes May Form Through Repeated Violent Collisions

Astronomers have uncovered new evidence suggesting that some of the Universe’s biggest black holes may not form directly from collapsing stars, but instead grow through repeated violent mergers inside densely packed star clusters.

The findings are based on a major international study analysing gravitational-wave signals detected across space, offering fresh clues into how supermassive black holes evolve over time.

Top Summary

• What happened: Scientists found evidence that massive black holes may grow through repeated mergers inside star clusters.
• Why it matters now: The discovery challenges traditional theories about how the Universe’s largest black holes form.
• What changes for people: The research could reshape scientific understanding of stellar evolution, gravity and cosmic formation.
• Who is affected: Astronomers, physicists, space researchers and gravitational-wave observatories worldwide.

The study analysed data from the LIGO–Virgo–KAGRA Collaboration gravitational-wave catalogue, which currently contains more than 150 confirmed black hole merger detections.

Researchers focused particularly on the heaviest black holes observed through gravitational-wave ripples — disturbances in spacetime created when massive cosmic objects collide.

According to the research team, these giant black holes likely formed through “hierarchical mergers,” a process where smaller black holes repeatedly collide and merge over time inside crowded stellar environments known as globular star clusters.

One such example highlighted in the study is M80, located around 28,000 light-years from Earth and containing hundreds of thousands of stars packed closely together.

Scientists say these extremely dense regions create ideal conditions for black holes to repeatedly collide and grow larger.

Lead researcher Fabio Antonini explained that gravitational-wave astronomy is now moving beyond simply detecting collisions and is beginning to reveal how black holes actually evolve.

The team identified two distinct black hole populations:

• Lower-mass black holes likely formed through normal stellar collapse
• Higher-mass black holes showing spin patterns consistent with repeated merger events

Researchers said the rapidly spinning and randomly oriented heavier black holes strongly support the theory that they formed inside dense star clusters rather than directly from dying stars.

The study also strengthens evidence for the long-theorised “pair-instability mass gap,” a mysterious mass range where extremely massive stars are expected to explode before they can collapse into black holes.

Scientists believe black holes above roughly 45 times the mass of the Sun should theoretically not form directly through standard stellar collapse processes.

However, gravitational-wave observations have detected black holes that appear to exist within or near this forbidden range.

Researchers now believe repeated mergers inside star clusters may explain how these unusually massive black holes formed.

Co-author Isobel Romero-Shaw said the distinction between ordinary black holes and the heavier rapidly spinning population became much clearer in newer gravitational-wave datasets.

Scientists also noted that future gravitational-wave observations may help researchers study nuclear reactions occurring deep inside massive stars, potentially improving understanding of stellar physics and cosmic evolution.

The findings were published in the journal Nature Astronomy.

Bottom line

The new study suggests that the Universe’s biggest black holes may grow through repeated violent mergers inside crowded star clusters rather than forming directly from stars. The discovery could significantly reshape scientific understanding of black hole formation and the evolution of massive cosmic objects.

What to watch next

• Future gravitational-wave detections from LIGO and Virgo
• Research into the black hole “mass gap”
• More evidence supporting hierarchical black hole mergers
• Advances in gravitational-wave astronomy
• How the findings influence theories of stellar evolution and galaxy formation