Scientists have solved the mystery surrounding the most massive black hole merger ever detected, revealing how two “impossible” black holes formed despite long-held assumptions that stars of that size should not exist. The collision, designated GW231123, involved two black holes weighing roughly 100 and 130 times the mass of our sun – falling within a previously thought “mass gap” where black holes shouldn’t exist.
The Impossible Black Hole Problem
For decades, astronomers believed that stars large enough to produce black holes of this magnitude would explode violently in supernovas, leaving no remnant capable of collapsing into a black hole. The discovery of GW231123 challenged this understanding, as it featured two such “forbidden” objects, both spinning at extreme speeds. This raised the question: how could these black holes form when they shouldn’t?
The Role of Rapid Rotation and Magnetism
The breakthrough came from detailed simulations that accounted for rapidly rotating, highly magnetized stars. Researchers found that as these stars collapse, strong magnetic fields within the core create powerful outflows, expelling much of the stellar material before it can fall into the forming black hole. This process reduces the final mass, pushing it into the previously inaccessible mass gap.
“We showed that if the star rotates rapidly, it forms an accretion disk around the newly born black hole. Strong magnetic fields generated within this disk can drive powerful outflows that expel part of the stellar material, preventing it from falling into the black hole.” — Ore Gottlieb, Center for Computational Astrophysics
The simulation also linked the final mass and spin of the black hole to the strength of its magnetic field. Stronger fields eject more material, resulting in a lower-mass, slower-spinning remnant. Weaker fields allow for greater mass retention, creating heavier, faster-spinning black holes. The properties inferred from GW231123 align perfectly with this model, suggesting that one black hole formed in a star with moderate magnetism, while the other came from a weaker field.
Implications for Gravity and Cosmic History
This discovery has profound implications. Extreme events like GW231123 push Einstein’s theory of general relativity to its limits, providing a testing ground for the theory in the most extreme gravitational environments. The ability to observe such mergers through gravitational waves – ripples in spacetime – offers a unique window into the universe where even light cannot escape.
Moreover, the new findings suggest that black holes may form more efficiently than previously thought. If this mechanism was common in the early universe, it could explain how the first generation of stars and black holes seeded the supermassive black holes found at the centers of galaxies today.
What’s Next?
The team’s work predicts that future gravitational-wave detections will reveal a clear correlation between black hole mass and spin. As more massive black hole binaries are discovered, scientists will test whether this relationship holds true across a larger population. If confirmed, it could validate the new formation pathway and uncover a hidden population of massive, rapidly spinning black holes. The collision of GW231123 may be just the first sign of a new era in black hole research.
