Analogy between spinning disks and merging black holes

On the analogy between spinning disks coming to rest and merging black holes

D. D. Meringolo, F. Conidi, A. Mercuri, M. Sposato, R. C. Barberi and G. Pucci

Am. J. Phys. 93, 551–556 (2025)

DOI: https://doi.org/10.1119/5.0208307

The characteristic motion of a disk as it spins and rolls without slipping on a surface before coming to rest is a daily-life phenomenon that exhibits interesting dynamics. In this work, we explore an analogy between the disk coming to rest and the merging of two black holes. By comparing the analytical descriptions of both systems, we highlight how the precession frequency of the disk and the orbital frequency of black holes exhibit a similar increase over time. Experimentally, we investigate the motion of the disk coming to rest by measuring the vertical vibrations induced in the supporting platform. These vibrations are related to the precession angular velocity of the disk. Notably, these vibrations share common features with the gravitational waves emitted by merging black holes, including their frequency and amplitude increasing with time. We conclude by examining both the strengths and limitations of this analogy and by presenting an open challenge for students to further explore these connections.