Black holes have long been understood as the final resting places of collapse, swallowing matter and merging with one another into ever larger singularities hidden behind their horizons. A new theoretical study in Physical Review D turns that familiar picture around, asking whether a single black hole could ever divide into two. The answer, for now, is a cautious and conditional maybe: entropy usually forbids such a split, spin may open a narrow door, and the pieces must still be able to drift apart rather than fall back together. The work leaves open how gravity behaves beyond Einstein's fram
Near-Maximally Spinning Black Holes Might Split in Two, Theoretical Study Suggests
The window largely closes again, except possibly for near-maximal spin
Mark
So what's the basic claim here? Black holes splitting in two?
Mimi
It's a question more than a claim. The authors ask what laws normally prevent a split, and whether any circumstances loosen those rules. The main barrier is entropy: for a non-rotating black hole, splitting would lower it.
Mark
And rotation is the loophole?
Mimi
Possibly. Fast-spinning black holes might get around the entropy problem. But the two pieces also have to separate instead of falling back together, and that largely shuts the window again.
Luke
Largely, not entirely. Sannino says the exception is black holes spinning close to their maximum rate, and he says "possibly." That's a hedge, not a finding.
Mark
Where does the pants image come from?
Mimi
The horizon, the black hole's outer boundary, would form a pants shape through time, one section dividing into two legs.
Mark
Do extra dimensions make it more likely?
Mimi
In those theories, splitting can become thermodynamically favorable, especially when one piece is much smaller than the other.
Luke
Favorable isn't the same as happening. The article says so directly. And there's no probability yet; Sannino says it depends on gravity beyond Einstein, which they're still trying to quantify.
Mark
Is there any way to test it?
Mimi
Sannino points to gamma-ray telescopes like Fermi-LAT searching for signals from tiny fragments formed in mergers.
Luke
Worth noting that's a suggestion for indirect detection. Nothing has been observed, and his expectation that small primordial black holes split more easily is an expectation, not a result.
O Pulso
- A physical rule that black holes almost never break apart is being tested against the possibility that spin changes everything.
- Thermodynamics pushes firmly against splitting, since two smaller black holes would carry less total entropy than one large one.
- Researchers are narrowing the escape route: rapid rotation offers a loophole, but the fragments must separate instead of re-merging.
- The window appears to close again except near maximum spin, and primordial black holes are seen as the most likely candidates, while experimental detection through gamma-ray searches remains indirect and unproven.
Black holes have long been understood as the final resting places of collapse, swallowing matter and merging with one another into ever larger singularities hidden behind their horizons. A new theoretical study in Physical Review D turns that familiar picture around, asking whether a single black hole could ever divide into two. The answer, for now, is a cautious and conditional maybe: entropy usually forbids such a split, spin may open a narrow door, and the pieces must still be able to drift apart rather than fall back together. The work leaves open how gravity behaves beyond Einstein's framework, a question that will decide how far that door truly swings.
A new paper in Physical Review D, titled "When Black Holes Admit Pair-of-pants Topologies," asks a question that runs against everything astronomers usually observe: can a black hole divide into two smaller ones? Black holes are known to collide and merge, but the reverse has never been seen, and the team set out to identify the laws that forbid it and any circumstances that might allow it. The work is led by Francesco Sannino, a physicist at the University of Naples Federico II and the Quantum Field Theory Center at the University of Southern Denmark, with co-authors Giacomo Cacciapaglia of CNRS and Sorbonne Université in Paris, and Manuel Del Piano and Vania Vellucci in Denmark.
The central obstacle is entropy, the measure of how many hidden microscopic arrangements a system can take. For an ordinary, non-rotating black hole, splitting would reduce total entropy, which is why nature does not do it. Rapid spin, however, appears to offer a loophole in that argument. Sannino stresses that entropy is only half the test: the two fragments must also be able to move apart rather than fall back together, and once that requirement is included, the opening largely shuts, perhaps leaving a sliver for black holes spinning near their maximum rate. The strange title refers to the shape the horizon would trace through time, a pants-like figure with one section dividing into two legs.
The authors also examine theories with extra spatial dimensions, where some black-hole-like objects are already known to become unstable. There, splitting can be thermodynamically favored, especially when one fragment is much smaller than the other, though favorable thermodynamics does not guarantee that fragmentation actually happens. Sannino is candid that the team cannot yet assign a probability, because the answer depends on gravity beyond Einstein's theory, which they are still working to quantify. He expects small primordial black holes to be the likeliest to split. A possible path to evidence lies in gamma-ray telescopes such as Fermi-LAT, which could search for signatures of tiny fragments produced in mergers. For now, the work remains theoretical, and its central question is how gravity behaves beyond Einstein's framework.
A new theoretical paper in Physical Review D asks a question that runs against what we usually see in the sky. Black holes collide and merge into one. Could a single black hole ever do the reverse and divide into two smaller ones? The study is titled "When Black Holes Admit Pair-of-pants Topologies," and its authors set out to work out which physical laws normally forbid such a split, and whether any circumstances might allow it.
The lead voice on the work is Francesco Sannino, a professor of physics at the University of Naples Federico II in Italy and at the Quantum Field Theory Center at the University of Southern Denmark. His co-authors are Giacomo Cacciapaglia, a CNRS researcher at the Laboratoire de Physique Théorique et Hautes Énergies in Paris, a joint laboratory of CNRS and Sorbonne Université, along with Manuel Del Piano and Vania Vellucci, both of the Quantum Field Theory Center in Denmark.
The main obstacle is thermodynamics. A black hole carries entropy, a measure of 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 smaller ones would lower the total entropy. That makes the process thermodynamically unfavorable, which is why black holes do not normally split.
Rotation changes the picture. The team's calculations indicate that rapidly spinning black holes offer a possible loophole in the entropy argument. But entropy is only part of the test. The two resulting black holes would also have to be able to move apart, rather than fall straight back together. Sannino says that once this requirement is included, the window largely closes again, except possibly for black holes rotating close to their maximum possible rate.
The paper's odd title describes the geometry of such an event. If a split occurred, the black hole's horizon, its outer boundary, would trace a pants-like shape through time, with one section dividing into two legs. Hence "pair-of-pants topologies."
The authors also look at more exotic territory. In theories with extra dimensions of space, physicists already know of black-hole-like objects that can become unstable and start to break apart. Under some of those conditions, splitting can become thermodynamically favorable, particularly when one of the resulting black holes is much smaller than the other. Even so, favorable thermodynamics does not show that fragmentation will actually occur.
Sannino is candid about the limits. The team cannot yet give a single probability for a black hole to split, he says, because the answer depends on how gravity behaves beyond Einstein's theory, and they are working to quantify that. He expects small primordial black holes to be more prone to splitting than much larger astrophysical ones.
There may be a way to look for evidence. Sannino suggests a split could be detected indirectly, since gamma-ray telescopes such as Fermi-LAT can search for signals from tiny black-hole fragments that might form during mergers. For now the work remains theoretical, and the open question is how gravity behaves beyond Einstein's framework.
Citações Notáveis
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, University of Naples Federico II
The two resulting black holes must be able to separate rather than fall back together, and that largely closes the window except possibly near maximum rotation.— Francesco Sannino (paraphrased)
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