In a landmark discovery in 2023, the LIGO-Virgo-KAGRA (LVK) Collaboration detected gravitational waves from the largest black hole merger ever recorded, an event dubbed GW231123. This record-breaking occurrence defied existing scientific models due to the immense masses and spins of the black holes involved. Now, new research from the Flatiron Institute is challenging our understanding of black hole formation, suggesting magnetic fields play a crucial role.
The study, published in The Astrophysical Journal Letters, presents groundbreaking simulations that reveal how these “impossible” black holes formed and eventually merged. The research team from the Flatiron Institute’s Center for Computational Astrophysics discovered that magnetic fields exert a significantly greater influence on black hole formation than previously believed.
Solving the Mystery of Black Hole Formation
Researchers developed detailed computer simulations to track the lifecycle of stars, observing how their deaths produced the two black holes detected in GW231123. These simulations revealed that magnetic fields, often overlooked in past studies, are key to understanding the origins of these massive cosmic entities.
“No one has considered these systems the way we did; previously, astronomers just took a shortcut and neglected the magnetic fields,” said lead author Ore Gottlieb, an astrophysicist at the CCA. “But once you consider magnetic fields, you can actually explain the origins of this unique event.”
The Black Hole Mass Gap Puzzle
The core of the puzzle lies in the fate of massive stars. Typically, such stars end their lives by collapsing into black holes after a supernova, but only under specific conditions. Stars within a certain mass range undergo pair-instability supernovae, which completely obliterate the star, leaving no remnant. The black holes detected in GW231123 fall within this expected mass gap.
“As a result of these supernovae, we don’t expect black holes to form between roughly 70 to 140 times the mass of the sun,” Gottlieb explains. “So it was puzzling to see black holes with masses inside this gap.”
One theory suggested that two smaller black holes merged to form the larger ones. However, this explanation faltered as both black holes in GW231123 exhibited extremely rapid spins, near the speed of light. Typically, a merger would result in a remnant with a disrupted or moderated spin, making this scenario unlikely.
Simulating the Birth of Black Holes
The researchers conducted their simulations in two stages. Initially, they modeled stars up to their final moments, focusing on stars with 250 solar masses that would burn down to about 150 solar masses before collapsing. At this mass, the resulting black hole would sit just above the upper boundary of the mass gap.
The second stage involved modeling the supernova remnants in detail. Prior models assumed that all surrounding stellar material would fall into the newly formed black hole. By incorporating magnetic fields, the researchers demonstrated that this assumption was incorrect.
The Role of Magnetic Fields
While non-rotating stars behaved as expected, rapidly spinning stars presented a different scenario. Their rotation formed a disk of stellar debris around the black hole, which accelerated as material fell inward. Eventually, the combination of the disk’s rotation and magnetic forces became strong enough to expel material outward at near light-speed.
Because so much mass is expelled rather than consumed, the resulting black hole ends up significantly lighter—potentially as little as half the mass of the collapsing star. This allows a black hole to form inside the mass gap while retaining a rapid spin.
“We found the presence of rotation and magnetic fields may fundamentally change the post-collapse evolution of the star, making black hole mass potentially significantly lower than the total mass of the collapsing star,” Gottlieb says.
Implications for Future Research
The study also identified a previously unrecognized relationship between a black hole’s mass and its spin. The researchers suggest that future observations of gamma-ray bursts could provide an opportunity to test their new model, potentially expanding our understanding of these powerful cosmic phenomena.
The paper, titled “Spinning into the Gap: Direct-horizon Collapse as the Origin of GW231123 from End-to-end General-relativistic Magnetohydrodynamic Simulations,” appeared in The Astrophysical Journal Letters on November 10, 2025.
This groundbreaking research not only challenges existing models of black hole formation but also opens new avenues for exploring the role of magnetic fields in the cosmos. As scientists continue to probe the mysteries of the universe, such discoveries will undoubtedly shape our understanding of the fundamental forces at play.
