Theoretical study explores conditions for black hole division

“Our study investigates the physical laws that normally prevent a black hole from splitting into two, and whether certain circumstances may allow a split to happen,” explained Francesco Sannino, a professor of physics at University of Naples Federico II in Italy and Quantum Field Theory Center at University of Southern Denmark, and co-author of the study. 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 in Paris, along with Manuel Del Piano and Vania Vellucci, both from the Quantum Field Theory Center at the University of Southern Denmark.

Typically, black holes remain intact due to thermodynamic constraints. Entropy, a measure of a system’s microscopic arrangements, limits changes to black holes; reducing entropy, as would occur if a non-rotating black hole were to split, is thermodynamically unfavorable.

However, the study suggests that extremely rapid rotation could create a loophole in these restrictions, potentially allowing a black hole to divide. Even then, the resulting black holes would need to separate to avoid immediate re-merger. “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,” Sannino stated.

The study’s title, “When Black Holes Admit Pair-of-pants Topologies,” refers to the shape of a black hole’s boundary during such a split, resembling a pair of trousers with a single structure dividing into two branches.

The researchers also considered theories involving extra spatial dimensions beyond the three we experience daily. In these models, black holes can become unstable and fragment. While thermodynamics might favor splitting under these conditions, it doesn’t guarantee it will occur.

Scientists are now working to determine the likelihood of these events, a challenge that may require exploring gravity beyond Einstein’s theory. “We cannot yet give a single probability for a black hole to split. It depends on how gravity behaves beyond Einstein’s theory, and we are working to quantify this,” Sannino said. He suggests that smaller, primordial black holes are more likely to split than larger astrophysical black holes, and that gamma-ray telescopes like Fermi-LAT could potentially detect signals from fragments resulting from such events.

Sannino is the director of the Quantum Field Theory Center (ℏQTC), which is affiliated with the Department of Mathematics and Computer Science (IMADA) at the University of Southern Denmark. He is also affiliated with the Danish Institute for Advanced Study and the Department of Physics “Ettore Pancini” at the University of Naples Federico II, and serves as a visiting professor at Durham University.