Magnetic Fields May Explain 'Impossible' Black Hole Merger GW231123
New simulations suggest strong magnetic fields during supernovae can push black holes into a previously forbidden mass gap.
Astronomers have identified a potential explanation for GW231123, a black hole merger that appeared to defy the known laws of stellar evolution. The event, occurring approximately 7 billion light-years away, involved two black holes that existed within a theoretical 'forbidden zone' of mass.
The merger is an anomaly because the black holes fell within the mass gap of roughly 70 to 140 solar masses. In this range, pair-instability supernovae typically result in the complete annihilation of the star, leaving no remnant behind. Furthermore, the black holes in GW231123 exhibited extreme spin rates, which LIGO researchers describe as some of the fastest ever observed.
The Physics of the Mass Gap
Standard models of stellar death suggest that stars within this specific mass range are too unstable to collapse into a single object. Instead, they undergo a violent explosion that destroys the entire star. While previous theories suggested that 'impossible' black holes might be second-generation objects formed from the merger of smaller black holes, that process typically scrambles the spin of the resulting object. The high spin rates of GW231123 made the second-generation theory unlikely, leaving scientists without a viable explanation for how these objects formed.
A Magnetic Solution
New simulations led by Ore Gottlieb at the Flatiron Institute provide a solution. The research suggests that strong magnetic fields during a supernova can fundamentally alter the outcome of a star's collapse. The spinning disk of a dying star normally feeds material into the black hole, but intense magnetic fields can exert enough pressure on this disk to eject significant stellar mass at nearly the speed of light. This mass ejection pushes the final black hole's mass down into the forbidden zone while allowing it to maintain an extreme spin.
Implications for Astrophysics
This discovery challenges existing models of how the universe's most massive objects are created. By demonstrating that magnetic fields can modulate both the final mass and the spin of a black hole, researchers have found a mechanism to populate the mass gap. This provides a new understanding of the interaction between magnetic forces and spacetime during the final moments of a massive star's life.
Future Observations
As gravitational wave detectors become more sensitive, astronomers will look for more events similar to GW231123 to verify if magnetic mass ejection is a common occurrence. Confirming this mechanism would require a broader sample of mergers within the 70 to 140 solar mass range to determine if high spin is a consistent signature of this process.