The Sound of an Orbit: A Quantum Spectrum at the ISCO
arXiv:2507.14254 · doi:10.1002/prop.70048
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 strong-field gravitational regime and provides a clear distinction between the quantum phenomena experienced by observers on different trajectories. Our findings have potential implications for interpreting the emission spectra from accretion disks and open new avenues for exploring the connection between quantum mechanics and gravity.
13 pages, 3 figures. Published version
References in corpus (8)
- How often does the Unruh-DeWitt detector click? Regularisation by a spatial profile
- Self-Force Calculations with Matched Expansions and Quasinormal Mode Sums
- Unruh-DeWitt detector response along static and circular geodesic trajectories for Schwarzschild-AdS black holes
- Unruh and analogue Unruh temperatures for circular motion in 3+1 and 2+1 dimensions
- Nonthermal acceleration radiation of atoms near a black hole in presence of dark energy
- Seeing dark matter via acceleration radiation
- Derivative coupling in horizon brightened acceleration radiation: a quantum optics approach
- Acceleration Radiation from Derivative-Coupled Atoms Falling in Modified Gravity Black Holes