--- title: "Physicists calculate conditions under which a black hole could split in two" description: "Italian, French, and Danish physicists have mathematically described a scenario where a near-maximally rotating black hole could split into two objects. The process is thermodynamically permissible only under extreme rotation; it remains a purely theoretical model." date: 2026-11-03T17:18:39.458Z lang: en url: https://xab.info/en/posts/physicists-calculate-black-hole-splitting-conditions tags: [black-hole, physics, general-relativity, entropy, primordial-black-holes, cosmology] author: "Alexander Buran" publisher: "XAB.info" --- # Physicists calculate conditions under which a black hole could split in two ![Artistic representation of two interacting black holes in space, resembling the infinity symbol.](https://xab.info/media/2026/11/03/fiziki-rasschatali-usloviya-raskola-chyornoy-dyry/fiziki-rasschatali-usloviya-raskola-chyornoy-dyry-1.webp) ## Key Points - A team of physicists from Italy, France, and Denmark calculated the theoretical conditions for a black hole to decay into two objects - The key condition is the original black hole's rotation being close to the maximum (Kerr limit) level - The event horizon geometry at the moment of decay is dubbed the "pair-of-pants topology" - For a stationary black hole, decay is thermodynamically prohibited due to a decrease in entropy - Primordial black holes from the early Universe have the highest chances of such decay - Traces of the process could be indirectly detected using gamma-ray telescopes like Fermi-LAT A group of theoretical physicists from Italy, France, and Denmark has published a study mathematically describing a scenario in which a black hole could theoretically split into two independent objects. The work, reported by RBC-Ukraine with reference to Universe Today, addresses one of the most fundamental problems of modern physics: the compatibility of thermodynamic constraints with the quantum-gravitational dynamics of compact objects. The authors—Francesco Sannino (University of Naples Federico II and the CP3-Origins Center at the University of Southern Denmark), Giacomo Cacciapaglia (Laboratory of Theoretical Physics and High Energy, LPTHE), and Manu Cennano (field theory)—have shown that under certain initial conditions, the decay is not only not prohibited but is thermodynamically permissible. ### "Pair-of-pants topology": the geometry of decay According to the mathematical calculations, at the moment of splitting, the event horizon of the original black hole takes on a shape resembling a pair of trousers: two "legs" correspond to the two new event horizons, and the crotch area represents the region where spacetime remains connected. This is why the researchers named this configuration a "pair-of-pants topology." This geometric structure is a key consequence of the fact that the decay process is not instantaneous but occurs through an intermediate state where the single singularity has not yet fully divided into two independent ones. ### Rotation as the only "key" to decay A critical condition without which the decay is impossible is the extremely rapid rotation of the original black hole. As Francesco Sannino explained, the initial black hole must rotate at nearly the maximum allowable speed—that is, be close to the Kerr limit, beyond which classical general relativity predicts the exposure of a naked singularity. Rotation alters the balance between the object's mass, angular momentum, and entropy: this shift is what allows it to overcome the thermodynamic barrier, which makes decay practically impossible for a stationary black hole. For a standard stationary black hole, splitting into two would lead to a decrease in the system's total entropy, violating the second law of thermodynamics. However, a rotating black hole possesses additional "freedom" in distributing angular momentum between two daughter objects, making the total entropy of the decay products no less than the entropy of the original body. ### The "no-remerge" condition and the role of momentum A second, equally important requirement derived by the authors is that the two newly formed black holes must fly apart in different directions immediately after splitting, with sufficient speed to prevent gravitational attraction from pulling them back into a single system. If conditions are ideal, the "twins" retain the initial momentum and velocity of the original object, causing their trajectories to diverge. Otherwise, calculations suggest that the two parts would quickly meet and re-merge, rendering the decay process reversible and, essentially, irrelevant in terms of observable physics. ### Primordial black holes as the most likely candidates The researchers emphasize that this is currently an exclusively theoretical concept; no such event has been recorded in the real cosmos. The precise probability of such a phenomenon cannot yet be calculated because it depends on how gravity operates in regimes beyond Einstein's general relativity—that is, on a yet-to-be-discovered theory of quantum gravity. Nevertheless, the authors point out that small primordial black holes, which may have originated in the first moments after the Big Bang, have orders of magnitude higher chances of decay than massive astrophysical objects, as their near-maximum rotation is achieved at significantly lower absolute values of angular momentum. ### How to detect traces of decay In the future, traces of such processes could be detected indirectly. Specifically, the researchers mention gamma-ray telescopes like Fermi-LAT, which are capable of detecting high-energy signals from tiny fragments formed during cosmic mergers and the splitting of compact objects. If a statistically significant anomaly in the gamma-ray spectrum is discovered in the data of such observatories—one that cannot be explained by standard models of accretion or mergers—it could become the first indirect evidence that black hole decay is not just a mathematical abstraction, but a real physical process occurring somewhere in the depths of the Universe. ## Fact-Check & Sources - [Черная дыра может расколоться пополам: почему это противоречит законам физики](https://www.rbc.ua/ukr/news/chorna-dira-mozhe-rozkolotisya-navpil-chomu-1793717526.html) - The source covers all key facts: the author group, topology name, rotation condition, thermodynamic argument, mention of primordial black holes, and Fermi-LAT. The text is fully consistent with the article's core. ## FAQ ### Can a black hole actually split into two parts? According to the calculations by the Italian, French, and Danish physics team, it is theoretically possible, but only if the initial black hole is rotating at nearly the maximum allowed speed. To date, no such event has been observed in space. ### Why can't a stationary black hole decay? Splitting a stationary black hole into two would lead to a decrease in the system's total entropy, which violates the second law of thermodynamics. Rotation changes the balance of mass, angular momentum, and entropy, making decay thermodynamically permissible. ### What is "pair-of-pants topology"? This is the name of the event horizon's geometric shape at the moment of decay: two "legs" correspond to two new black holes, and the middle part is the region where spacetime is still connected. The term was coined by the researchers to describe the intermediate configuration. ### How can traces of black hole decay be detected? The researchers point to the potential for indirect detection using gamma-ray telescopes like Fermi-LAT, which can record high-energy signals from fragments formed during the splitting of compact objects. ### Which black holes are most prone to decay? According to the authors, small primordial black holes that emerged in the early Universe have significantly higher chances of decay than massive astrophysical objects, as their maximum rotation limit is reached at lower absolute values of angular momentum.