In 2023, the LIGO-Virgo-KAGRA (LVK) Collaboration made a groundbreaking discovery by detecting gravitational waves from the largest black hole merger ever recorded, known as GW231123. This event not only shattered records but also challenged existing scientific models due to the extraordinary masses and spins of the black holes involved.
Now, researchers from the Flatiron Institute are reshaping our understanding of black hole formation through an innovative study that highlights the significant role of magnetic fields in these cosmic phenomena.
Unraveling the Mystery
In a recent paper published in The Astrophysical Journal Letters, the Flatiron Institute’s Center for Computational Astrophysics revealed how these “impossible” black holes came into existence and ultimately merged. The team utilized detailed computer simulations to track the lifecycle of stars, discovering that magnetic fields exerted a much greater influence than previously acknowledged.
“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.”
Black Hole Formation Challenges
The core of the puzzle lies in understanding how massive stars end their lives. Typically, such stars collapse into black holes following a supernova, but only under specific conditions. Stars within a certain mass range undergo pair-instability supernovae, which completely destroy the star, leaving no remnants. The black holes detected in GW231123, however, exist 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 hypothesis suggested that two smaller black holes merged, but this theory faced challenges due to the rapid spins of both black holes in GW231123, which were near the speed of light. Typically, a merger results in a remnant with a disrupted or moderated spin, making this scenario unlikely.
Simulating Black Hole Births
The researchers conducted their simulations in two stages. Initially, they modeled stars up to their final moments, focusing on stars with 250 solar masses, which would reduce to about 150 solar masses by the time they collapsed. 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. Previous models assumed that all surrounding stellar material would fall into the newly formed black hole. By incorporating magnetic fields—often overlooked in such simulations—the researchers demonstrated that this assumption was flawed.
Impact 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 eject material outward at near light-speed.
“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 notes.
This ejection of mass results in a black hole that forms within the mass gap while maintaining a rapid spin. The study also uncovered a previously unrecognized relationship between a black hole’s mass and its spin.
Future Implications and Observations
The findings from this study open new avenues for understanding black hole formation and evolution. Future observations of gamma-ray bursts may provide opportunities to test this new model, potentially expanding our knowledge 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,” was published in The Astrophysical Journal Letters on November 10, 2025.
As the scientific community continues to explore these findings, the role of magnetic fields in cosmic events may become a pivotal factor in the study of astrophysics, challenging long-held assumptions and paving the way for new discoveries.
