Black holes are known for merging when two of them collide, but could the reverse ever happen? Could a single black hole somehow divide into two smaller ones? A new theoretical study suggests that this extraordinary possibility may not be entirely ruled out by physics, although the conditions required would be extreme.
The research, published in Physical Review D under the title "When Black Holes Admit Pair-of-pants Topologies," examines the physical laws that keep black holes intact and whether certain circumstances could allow them to break apart. "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 University of Naples Federico II in Italy and Quantum Field Theory Center at University of Southern Denmark.
The research team also included Giacomo Cacciapaglia, a researcher with the French National Centre for Scientific Research (CNRS) at the Laboratoire de Physique Théorique et Hautes Énergies, a joint CNRS and Sorbonne Université laboratory in Paris. Additional contributors were Manuel Del Piano and Vania Vellucci, both from the Quantum Field Theory Center at the University of Southern Denmark. Why Black Holes Normally Cannot Split Apart One of the biggest obstacles to a black hole splitting comes from thermodynamics, the branch of physics that governs how energy behaves and how physical systems change.
A central concept is entropy, which describes how many different microscopic arrangements a system can have while appearing unchanged from the outside. Black holes have entropy, and this property places important limits on what can happen to them. For a black hole that is not rotating, dividing into two smaller black holes would reduce the total entropy.
Such a decrease makes the process thermodynamically unfavorable, helping explain why black holes do not ordinarily break apart. However, the researchers found that the situation could change dramatically when a black hole spins at an exceptionally high speed. Extreme Rotation Could Allow Black Holes to Split The team's calculations suggest that rapid rotation may create a narrow opening in the physical rules that normally prevent black holes from dividing.
In principle, a sufficiently fast spinning black hole could overcome the usual thermodynamic restriction. But there is another major obstacle. Even if a black hole could divide, the two resulting objects would need to move far enough apart to avoid immediately merging again.
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