Spectral Lines of Quantized, Spinning Black Holes and their Astrophysical Relevance

Abstract

In this Letter, we study black hole area quantization in the context of gravitational wave physics. It was recently argued that black hole area quantization could be a mechanism to produce so-called echoes as well as characteristic absorption lines in gravitational wave observations of merging black holes. One can match the spontaneous decay of these quantum black holes to Hawking radiation calculations. Using some assumptions, one can then estimate the natural widths of these states. As can be seen from a classical paper by Bekenstein and Mukhanov, the ratio between width and spacing of nonspinning black hole states approaches a small constant, which seems to confirm the claim. However, we find that, including the effect of black hole spin, the natural widths increase. To properly address any claim about astrophysical black holes, one should examine the spinning case, as real black holes spin. Thus, the word spinning is key to the question of whether or not black holes should have an observable spectrum in nature. Our results suggest that it should be possible to distinguish between any scenarios for which the answer to this question is yes. However, for all of the commonly discussed scenarios, our answer is almost certainly no.

5 pages, 1 figure, minor changes for clarity and some additional references

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• On Black Hole Area Quantization and Echoes
• Probing the quantum nature of black holes with ultra-light boson environments
• Fractional Schwarzschild-Tangherlini black hole with a fractal event horizon
• Echoes from beyond: Detecting gravitational-wave quantum imprints with LISA
• Formation and Stability of Area Quantized Black Holes
• Inverse problem of analog gravity systems II: Rotation and energy-dependent boundary conditions
• Spectral instability of horizonless compact objects within astrophysical environments
• Signatures of Quantum Gravity in Gravitational Wave Memory
• Superradiant instability of area quantized Kerr black hole with discrete reflectivity
• Absorption spectroscopy of quantum black holes with gravitational waves