Ore Gottlieb / Simons Foundation
Computer simulation of the formation and evolution of a black hole
A team of astrophysicists has discovered that magnetic fields play a decisive role in the formation of black holes that, until now, were considered impossible.
An extensive series of computer simulations, conducted by astrophysicists at the Flatiron Institute and collaborators, revealed that magnetic fields are the missing element in the creation of black holes whose masses fall within a range previously thought cannot exist.
In 2023, astronomers witnessed a dramatic event: two black holes extraordinarily massive collided about 7 billion light years away.
Its enormous size and extremely fast rotation contradicted all existing explanations. According to current theories, black holes like these they simply shouldn’t exist.
Researchers at the Center for Computational Astrophysics (CCA), the Flatiron Institute, and partner institutions have now discovered how these cosmic giants can form and end up colliding.
The discovery was presented in a publication on Monday in the journal The Astrophysical Journal Letters.
By reconstructing the life cycle of the stars that gave rise to them, the team concluded that the magnetic fieldslong neglected in previous models, are decisive.
“Nobody had looked at these systems the way we did; Until now, astronomers simplified and basically ignored magnetic fields,” he says. Ore Gottliebastrophysicist at CCA and main author of the article, in .
“But When magnetic fields are taken into account, it is possible to explain the origin of this singular event”, adds the researcher.
The 2023 collision that challenged black hole theory
A, today called GW231123was detected by the LIGO-Virgo-KAGRA observatories, which measure gravitational waves, the ripples in space-time produced by large-scale celestial movements.
At the time of detection, astronomers couldn’t understand how black holes so massive and so fast had formed. When a very massive star runs out of fuel, it collapses and explodes as a supernova, leaving behind a smaller black hole.
However, stars within a specific mass range experience a particularly violent type of explosion, called pair instability supernovawhich destroys the star completely.
“Because of these supernovae, we don’t expect black holes to form between about 70 and 140 times the mass of the Sun“, explains Gottlieb. “So it was surprising to observe black holes with masses within this range.”
One possible explanation is that black holes in this “forbidden mass range” form indirectly, through the merger of black holes smaller.
But in the case of GW231123, such a hypothesis seemed unlikely. Mergers are typically chaotic and tend to disrupt the rotation of the resulting black hole.
However, the two black holes involved in GW231123 were rotating at almost the speed of light, the fastest rotation ever observedmaking this scenario difficult to sustain.
To solve the puzzle, Gottlieb and his team performed a two-phase simulation. First, modeled a star with 250 solar masses throughout his life and death. By the time it exploded as a supernova, it had already burned enough fuel to shrink to around 150 solar masses — slightly above the theoretical forbidden range — giving rise to a black hole.
The next phase introduced magnetic fields. The model started with the supernova debris: a rotating cloud composed of stellar debris, containing magnetic fields and a newly formed black hole at the center.
Previous models assumed that all remaining material would eventually fall into the black hole, but the new simulations revealed another realityobserves .
How magnetism alters the fate of a collapsing star
If a collapsing star is not rotating, the surrounding matter falls directly into the black hole. But when the star rotates quicklythis matter forms a disk around the black hole, feeding it over time and increasing its rotation.
However, magnetic fields disrupt this process. Its pressure can expel part of the material at speeds close to light, preventing it from falling.
This expulsion reduces the amount of mass absorbed through the black hole. The stronger the magnetic fields, the more matter is launched into space. In extreme cases, up to half of the star’s original mass can be lost in these outflows.
In the team’s simulations, this mechanism naturally produced a black hole whose mass was precisely within the range considered “prohibited”.
“We discovered that the presence of rotation and magnetic fields can fundamentally alter the post-collapse evolution of the star, making the final mass of the black hole much less than the total mass of the collapsing star”, explica Gottlieb.
The results point to a intriguing relationship between the mass of a black hole and how fast it rotates. Stronger magnetic fields can halt the rotation and remove more stellar mass, resulting in smaller, slower black holes. Weaker fields allow the growth of heavier, faster-rotating black holes.
This pattern may reveal a broader relationship between mass and rotation — something that future observations can confirm.
At the moment, no other black hole systems are known to test this connection, but astronomers hope that future detections will reveal more examples similar to GW231123.
Simulations also suggest that these magnetic processes produce bursts of gamma rays during the formation of black holes. Detecting these emissions could help confirm the theory and show how common these massive black holes could be.
If confirmed, these discoveries not only explain a collision considered “impossible”, but could profoundly transform the way scientists understand some of the most extreme and fascinating objects of the universe.
