The Sound of an Orbit: A Quantum Spectrum at the ISCO
Reggie C. Pantig, Ali \"Ovg\"un

TL;DR
This paper uncovers a unique quantum spectral signature at the ISCO of a black hole, revealing a discrete frequency comb that differs from thermal spectra, offering new insights into quantum gravity effects near black holes.
Contribution
It introduces a novel quantum detector model at the ISCO, demonstrating a non-thermal, discrete spectral signature that distinguishes quantum effects on different trajectories in strong gravity.
Findings
Discovery of a discrete frequency comb in the excitation spectrum at the ISCO
Peak locations are determined by the orbital frequency
Spectral intensity increases near the stability boundary
Abstract
We investigate the quantum signature of the innermost stable circular orbit (ISCO), a region of profound importance in black hole astrophysics. By modeling an atom as an Unruh-DeWitt detector coupled to a massless scalar field in the Boulware vacuum, we calculate the excitation rate for a detector following a circular geodesic at the ISCO of a Schwarzschild black hole. In stark contrast to the continuous thermal spectra associated with static or infalling observers, our analysis reveals a unique, non-thermal excitation spectrum characterized by a discrete "frequency comb" of sharp, resonant peaks. We show that the locations of these peaks are determined by the orbital frequency at the ISCO, while their intensity increases dramatically as the orbit approaches this final stability boundary. This distinct spectral signature offers a novel theoretical probe of the quantum vacuum in a…
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Taxonomy
TopicsQuantum Electrodynamics and Casimir Effect · Astrophysical Phenomena and Observations · Pulsars and Gravitational Waves Research
