Deciphering the Instability of the Black Hole Ringdown Quasinormal Spectrum

Area of Science:

• Astrophysics
• Gravitational Wave Astronomy
• Black Hole Physics

Background:

• The ringdown phase of black hole mergers emits gravitational waves.
• The spectrum of these gravitational waves is crucial for understanding black hole mergers.
• This spectrum is highly sensitive to system disturbances, posing challenges for predictions.

Purpose of the Study:

• To provide an analytical and intuitive explanation for the instability in the gravitational wave ringdown spectrum.
• To analyze the properties of this instability.
• To interpret the robustness of specific gravitational wave observables.

Main Methods:

• Utilizing the transfer matrix approach from quantum mechanics.
• Analyzing the sensitivity of the quasinormal mode spectrum to perturbations.
• Investigating the corrections to time-domain ringdown signals and greybody factors.

Main Results:

• An analytical explanation for the instability in the gravitational wave spectrum is presented.
• The properties of this instability are characterized.
• Parametrically small corrections to prompt ringdown and greybody factors are identified.

Conclusions:

• The transfer matrix method offers an intuitive understanding of ringdown spectral instabilities.
• Prompt ringdown signals and black hole greybody factors are robust observables despite spectral sensitivity.
• This work enhances the predictability of gravitational wave signals from black hole mergers.