In 2023, astronomers detected one of the most extraordinary cosmic events ever seen — a collision between two enormous black holes, located about seven billion light-years away.
The signal, named GW231123, was captured by the LIGO-Virgo-KAGRA network, which listens for gravitational waves, or ripples in space-time caused by the movement of very massive objects.
This discovery puzzled scientists because the two black holes were far larger and spun much faster than any black holes of their kind ever observed. According to existing theories, black holes of this size were not supposed to exist at all.
Now, researchers from the Flatiron Institute’s Center for Computational Astrophysics (CCA) believe they’ve found the missing piece of the puzzle.
Using advanced computer simulations, the team traced how these black holes could have formed from the birth of massive stars to their explosive deaths. Their results point to something that earlier studies had overlooked — magnetic fields.
‘No one had looked at these systems the way we did,’ said Ore Gottlieb, the lead scientist of the study. ‘In the past, astronomers ignored magnetic fields because they thought they were too weak to matter. But once we included them, everything suddenly made sense.’
To understand why this discovery is so important, it helps to know how black holes usually form. When very large stars reach the end of their lives, they often collapse under their own gravity and explode in a supernova.
The leftover core becomes a black hole. However, for stars within a certain mass range — about 70 to 140 times the mass of the Sun — something different happens. These stars explode in what’s called a pair-instability supernova, which is so violent that it completely destroys the star, leaving no black hole behind.
Because of this, astronomers believed there should be a ‘mass gap’ — a range where no black holes exist. The two colliding black holes in GW231123, however, fell right into that forbidden range, making their existence a major mystery.
Some scientists suggested these massive black holes might have formed from earlier black hole mergers. But that explanation didn’t fit. When black holes merge, the resulting object’s spin usually slows down, yet the black holes in GW231123 were spinning near the speed of light — the fastest ever recorded by LIGO.
Gottlieb’s team began testing other ideas using powerful computer simulations. First, they modeled the life of a huge star about 250 times heavier than the Sun. As the star aged, it burned its fuel and eventually slimmed down to around 150 solar masses — just above the supposed mass gap. When it collapsed, it created a black hole.
The second part of the simulation looked at what happened after the collapse. This time, the researchers included magnetic fields, which changed everything.
Without magnetic fields, scientists assumed nearly all the leftover gas and debris would fall into the black hole, making it very heavy. But when magnetic fields were added, they created strong forces that pushed some of this material away at nearly the speed of light.
In other words, magnetic pressure caused part of the star’s material to escape instead of falling into the black hole. The stronger the magnetic field, the more material was ejected. In extreme cases, up to half of the star’s mass could be blown away.
This explained how black holes could form in the mass gap while still being fast-spinning — something earlier theories could not account for.
The team also found that the strength of magnetic fields might determine a black hole’s final mass and spin. Stronger fields tend to produce smaller, slower-spinning black holes, while weaker fields create heavier, faster-spinning ones. This discovery could mean that there’s a hidden pattern connecting how heavy and how fast black holes are.
Another interesting result from the simulations was the prediction that such black hole births should release intense flashes of gamma rays — the most energetic form of light in the universe. If astronomers can detect these gamma-ray signals in the future, they might be able to confirm this new theory about how massive black holes form.
Overall, this research helps fill in one of the biggest gaps in our understanding of black holes. It shows that magnetic fields, often ignored before, can play a critical role in shaping how the universe’s most mysterious objects are born and evolve. It also opens the door for future discoveries, as scientists search the skies for more of these extreme events.
The study is published in The Astrophysical Journal Letters.
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