Black holes have long been understood as the most final of cosmic objects, swallowing whatever crosses their boundaries and growing by merging with one another. A team of European physicists, led by Francesco Sannino, has now worked through the hypothetical opposite: a single black hole dividing into two. Their calculations suggest this could happen only under demanding conditions, chiefly very rapid rotation, and the idea remains unseen and unproven. It stands as a reminder that even the apparent certainties of gravity still hold open questions waiting to be asked.
Could a Black Hole Split in Two? European Physicists Map the Conditions
A black hole's pieces must separate, or fall straight back together
Mark
Black holes are supposed to be the ultimate one-way trap. Why would anyone study splitting one?
Mimi
Because the calculation tests what the physics permits. The team asked under what conditions a black hole could divide into two, and they found a narrow set of them.
Mark
What's the main thing standing in the way?
Mimi
Entropy. For a non-rotating black hole, splitting would lower it, which makes the process thermodynamically unlikely.
Luke
Worth saying plainly: this is a theoretical result. Nobody has seen a black hole split, and the reporting offers no observation behind it.
Mark
So where does spin come in?
Mimi
Rotation changes how mass, angular momentum and entropy relate to one another. That could make fragmentation possible. But the two pieces also have to separate instead of falling back together.
Luke
And that requirement shrinks the window a lot. Sannino says it largely closes except possibly for holes spinning near their maximum rate. So this is a narrow case.
Mark
Does M87 count?
Mimi
Its black hole has a measured spin, so the article says that in theory it could break apart if conditions were right. That's a statement of possibility, not a prediction.
Luke
Right. And Sannino says there's no single probability yet, because it depends on how gravity behaves beyond Einstein's theory. That part is unresolved.
Mark
Is there any way to check?
Mimi
He expects small primordial black holes to split more readily, and suggests Fermi-LAT might catch gamma-ray signals from tiny fragments formed in mergers.
Luke
That's a hope for indirect detection, stated as 'might.' No such signal has been reported.
Der Puls
- A single black hole, once thought to be indivisible, may be able to split in two under extreme spin.
- The event horizon would take on a trouser-like shape, a 'pair-of-pants topology' that has never been witnessed.
- Entropy works against the split for ordinary black holes, so the process appears thermodynamically unlikely.
- The two fragments must spin near their maximum rate and fly apart quickly, or they would fall back together.
- Researchers hope tiny primordial black holes and gamma-ray telescopes like Fermi-LAT could reveal the process indirectly.
Black holes have long been understood as the most final of cosmic objects, swallowing whatever crosses their boundaries and growing by merging with one another. A team of European physicists, led by Francesco Sannino, has now worked through the hypothetical opposite: a single black hole dividing into two. Their calculations suggest this could happen only under demanding conditions, chiefly very rapid rotation, and the idea remains unseen and unproven. It stands as a reminder that even the apparent certainties of gravity still hold open questions waiting to be asked.
Black holes merge, and each merger sends gravitational waves rippling through space. Because their gravity is so overwhelming, it is hard to imagine anything tearing one apart. A European group set out to test that intuition anyway.
Led by Francesco Sannino, with Giacomo Cacciapaglia, Manuel Del Piano and Vania Vellucci, the team worked out that under the right conditions a single black hole could divide into two. Its event horizon would briefly take the form of a pair of trousers, with two legs branching from one waist. No one has seen this, so the result remains theoretical.
The obstacle is entropy. For a non-rotating black hole, splitting would reduce entropy, making it highly improbable. Rapid spin changes that balance, but the resulting pieces must also separate, or they would simply fall back together. Sannino's analysis suggests this window narrows to black holes spinning close to their limit.
Even the supermassive black hole at the heart of M87 has a measured spin, so in principle it could split. The team considers such events fairly rare among ordinary black holes, and no single probability has yet been given. Sannino expects the smallest primordial black holes to be most prone to splitting, and suggests gamma-ray observatories such as Fermi-LAT might one day catch faint signals of the tiny fragments.
Black holes merge. It has been happening since the first of them formed early in cosmic time, and each merger sends out gravitational waves in a violent burst. Because their gravity is so strong, it is hard to picture any force that could pull one apart. A group of physicists in Europe set out to work through the question anyway.
The team is led by Francesco Sannino, who holds posts at the University of Naples Federico II in Italy and at the Quantum Field Theory Center at the University of Southern Denmark. He worked with Giacomo Cacciapaglia of the Laboratoire de Physique Théorique et Hautes Énergies, along with Manuel Del Piano and Vania Vellucci, both of the Quantum Field Theory Center. Their calculations show that under the right conditions, a single black hole could divide into two. The researchers describe it as unusual, but they have worked out what would have to happen for it to occur.
The shape of the event horizon during such a split gives the idea its name. As the division proceeded, the horizon would take on a trouser-like form, with two legs branching from a single waist. The team calls this a pair-of-pants topology.
No one has observed such an event, so the work remains largely theoretical. The main obstacle is entropy, which measures how many different microscopic arrangements a system can have while looking the same from outside. For an ordinary, non-rotating black hole, splitting into two would lower its entropy. That makes the process thermodynamically unlikely.
Spin changes the picture. According to the team, a black hole rotating very rapidly could break into two pieces, because rotation alters the relationship between the hole's mass, its angular momentum and its entropy. That shift might open a path to fragmentation. The pieces would then have to move apart and carry on with the momentum and speed of the original.
They would also have to get away from each other. Sannino said the two resulting black holes must be able to separate rather than fall straight back together. Once that requirement is included, he said, the window largely closes again, except possibly for black holes rotating close to their maximum possible rate. In practice, both fragments would need to keep spinning at or near that limit.
The article notes that the black hole at the center of the galaxy M87 has a measured spin, so in principle, if conditions were right, it could break apart. Even so, the researchers consider such events among ordinary black holes fairly unlikely, though they stop short of saying one has never happened.
Sannino said no single probability can yet be given. It depends on how gravity behaves beyond Einstein's theory, which the team is working to quantify. He expects small primordial black holes to be more prone to splitting than much larger astrophysical ones. He also pointed to a possible way to look: gamma-ray telescopes such as Fermi-LAT could search for signals from tiny black-hole fragments that might form during mergers, which would offer an indirect detection.
Bemerkenswerte Zitate
We cannot yet give a single probability for a black hole to split. It depends on how gravity behaves beyond Einstein's theory.— Francesco Sannino
The two resulting black holes must be able to separate rather than immediately fall back together, which largely closes the window except possibly for near-maximally rotating black holes.— Francesco Sannino (paraphrased)
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