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

TL;DR

This paper investigates whether spinning black holes exhibit observable spectral lines due to area quantization, concluding that such features are unlikely to be detectable in realistic astrophysical scenarios.

Contribution

It extends previous nonspinning black hole models to include spin effects, showing that spin increases the widths of quantum states, reducing the likelihood of observable spectral lines.

Findings

Including spin increases the natural widths of black hole quantum states.

Observable spectral lines are unlikely in most realistic black hole scenarios.

The results challenge claims that black hole area quantization produces detectable echoes.

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.