Physics | 2021
Instability in Black Hole Vibrational Spectra
Abstract
A re black holes stable when they are slightly perturbed? This question was answered 50 years ago by the physicist C. V. Vishveshwara with a numerical experiment: Vishveshwara imagined sending a wave packet toward a black hole and observing what came out [1]. He found that the scattered wave is a sum of damped sinusoids, whose frequencies and damping times are the free-vibrationmodes, or so-called quasinormal modes, of the black hole. The damping implies that black holes are stable—they settle back into a stationary state after being perturbed. In a new study [2], José Luis Jaramillo from the University of Bourgogne Franche-Comté, France, and colleagues ask another important question: is the black hole quasinormal mode spectrum itself stable? If the black hole environment is perturbed in a small way by, for example, a small accretion disk, will the spectrum of the black hole change by just a tiny bit or by a disproportionally large amount? The surprising answer is that the spectrummay change by a lot, meaning that it is unstable. This instability may have important implications for interpreting gravitational-wave observations and for developing models of quantum gravity.