Bound States of the Schwarzschild Black Hole

TL;DR

This paper investigates the energy levels and eigenfunctions of Schwarzschild black holes by relating quasinormal modes to bound states in an inverted potential, revealing insights into their stability and physical interpretation.

Contribution

It is the first to quantitatively analyze bound states of Schwarzschild black holes, linking quasinormal modes with bound state spectra and exploring their stability and localization properties.

Findings

Eigenfunctions of quasinormal mode overtones become delocalized and loosely bound.

Bound states offer new perspectives on the spectral stability of black holes.

The study challenges traditional interpretations of quasinormal modes as localized excitations.

Abstract

Understanding the physical significance and spectral stability of black hole quasinormal modes is fundamental to high-precision spectroscopy with future gravitational wave detectors. Inspired by Mashhoon's idea of relating quasinormal modes of black holes with their equivalent bound states in an inverted potential, we investigate, for the first time, energy levels and eigenfunctions of the Schwarzschild black hole quantitatively. While quasinormal modes describe the characteristic damped oscillations of a black hole, the bound states of the inverted potential are qualitatively more similar to those of the hydrogen atom. Although the physical interpretation of these states may initially be of more academic interest, it furthers our understanding of open problems related to quasinormal modes in a similar spirit to Maggiore's interpretation of the Schwarzschild quasinormal mode spectrum. One surprising insight from the explicit calculation of bound states is that eigenfunctions corresponding to quasinormal mode overtones become rapidly delocalized and extremely loosely bound. This observation raises immediate questions about the common interpretation of quasinormal modes as excitations of the lightring region. Closely related, as a second application, we also explore the spectral stability of bound states and demonstrate that they can provide complementary insights into the quasinormal mode spectrum.