This article has been reviewed according to Science X's editorial process and policies. Editors have highlighted the following attributes while ensuring the content's credibility: Two black holes can collide and merge into one. But could the opposite happen: could a single black hole split into two smaller ones?
That question is explored in a new theoretical study: "When Black Holes Admit Pair-of-pants Topologies," published in the journal Physical Review D. "In our study, we investigate which physical laws normally prevent a black hole from splitting into two. We also investigate if certain circumstances may allow a split to happen," says Francesco Sannino, co-author of the study and a professor of physics at the University of Naples Federico II in Italy and the Quantum Field Theory Center at the University of Southern Denmark.
Co-authors are Giacomo Cacciapaglia, a Centre National de la Recherche Scientifique (CNRS) researcher at the Laboratoire de Physique Théorique et Hautes Énergies, a joint CNRS–Sorbonne Université laboratory in Paris, and Manuel Del Piano and Vania Vellucci, both from the Quantum Field Theory Center, University of Southern Denmark. Black holes do not normally split. One important obstacle preventing this comes from thermodynamics.
A black hole has what physicists call entropy. Put simply, entropy is a measure of how many different microscopic ways a physical system can be arranged while still appearing the same from the outside. For an ordinary, non-rotating black hole, splitting into two smaller black holes would reduce the total entropy.
That makes the process thermodynamically unfavorable. But things might be different with rapidly rotating black holes. The team's calculations show that rapidly rotating black holes provide a possible loophole allowing for a split to happen.
"But the two resulting black holes must also be able to separate rather than immediately fall back together. When we include this requirement, the window largely closes again, except possibly for black holes rotating close to their maximum possible rate," says Sannino. If such a split did occur, the black hole's outer boundary, known as the horizon, would form a pants-like shape through time: one section dividing into two "legs." This explains the study's unusual term "pair-of-pants topologies." The authors also explore more exotic possibilities.
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