A black hole is like a spinning top: the faster it spins, the more noticeable its behavior. It has two boundaries — the outer and inner horizons, the edges beyond which even light cannot return. In the new work, physicists looked inside a rotating charged black hole and multiplied the areas of these two surfaces.
This is not just number crunching. The constancy of the area product, and hence of entropy, a measure of disorder, allows connecting the black hole to a two-dimensional quantum field theory on its horizon. The scientists calculated the central charges of this theory — quantities that govern the symmetries of the system. And here everything reduced to rotation: the charges depend only on the angular momentum. Even for a stationary but charged black hole, they managed to find a nonzero charge using the same approach.
Such universality is rare. For comparison, they took another type of hole, Kerr-Newman, and saw that the difference hides in the "right" sector of the quantum theory.
as written by the authors arXiv:2606.14834
We explore the properties of inner and outer horizon thermodynamics of dyonic Kerr-Sen black hole (DKSBH). It is observed that the entropy (or area) product is universal, depending only on the angular momentum of the BH. We then proceed to study the dual conformal field theory~(CFT) in the Kerr/CFT correspondence using thermodynamic relations and compute the central charges from 2D CFT. The central charges are found to be universal with only angular momentum dependence. By comparing to Kerr-Newman BH, it is found that the essential difference is in the right-moving sector of the CFT. Interestingly, we can then explicitly produce the non-vanishing central charges related to its static solution, the dyonic dilaton BH, using the thermodynamic method. Moreover, from the CFT relations to multi-horizon thermodynamics, we find the analytical expression of the quasi-normal modes~(QNM) spectra in terms of BH parameters.
The product of horizon areas for some black holes does not change under any transformations, like a bank account where the sum on two accounts is always constant.
In the novel "Light of Distant Stars," the heroes calculate a black hole's history from its oscillations — much like in this work.