From Black Hole Spectral Instability to Stable Observables.

Area of Science:

• Theoretical physics
• Black hole physics
• Gravitational wave astronomy

Background:

• Black hole quasinormal modes (QNMs) are sensitive to potential perturbations, impacting observable time signals.
• Observing these subtle signals and probing QNM instability presents significant experimental challenges.

Purpose of the Study:

• Investigate the spectral instability of black hole properties using time-independent data.
• Explore the behavior of Regge poles (RPs) as counterparts to QNM in the complex angular momentum plane.

Main Methods:

• Analysis of spectral instability in time-independent data.
• Study of Regge poles (RPs) in the complex angular momentum plane.
• Examination of scattering quantities under spectral perturbations.

Main Results:

• Evidence of spectral instability in the Regge pole (RP) spectrum.
• Identification that not all overtones are equally affected by the instability.
• Discovery of an underlying structure that stabilizes scattering quantities despite RP spectrum perturbations.

Conclusions:

• A novel approach to black hole spectral instability phenomena is proposed.
• A surprising mechanism protects scattering quantities from instability, offering new avenues for research.
• The complex angular momentum approach provides stable scattering quantities even with spectral instability.