Spectroscopy of the quantum black hole

TL;DR

This paper proposes that quantum black holes have a discrete, broad spectral line emission pattern due to horizon fluctuations, linking spectral features to black hole entropy and enabling tests of quantum gravity.

Contribution

It introduces a model predicting discrete spectral lines for quantum black holes based on horizon fluctuations and level degeneracy, connecting spectral features to black hole entropy.

Findings

Black holes have a discrete mass spectrum with broad, unblended spectral lines.

Spectral line intensities depend on quantum transition probabilities and degeneracy.

No spectral lines are expected at wavelengths comparable to or larger than the black hole size.

Abstract

We develop the idea that, in quantum gravity where the horizon fluctuates, a black hole should have a discrete mass spectrum with concomitant line emission. Simple arguments fix the spacing of the lines, which should be broad but unblended. Assuming uniformity of the matrix elements for quantum transitions between near levels, we work out the probabilities for the emission of a specified series of quanta and the intensities of the spectral lines. The thermal character of the radiation is entirely due to the degeneracy of the levels, the same degeneracy that becomes manifest as black hole entropy. One prediction is that there should be no lines with wavelength of order the black hole size or larger. This makes it possible to test quantum gravity with black holes well above Planck scale.