Imperfect draining vortex as analogue extreme compact object

Abstract

Motivated by recent experimental progress, we study scalar wave propagation over an imperfect draining vortex, which can serve as an analogue for rotating and non-rotating extreme compact objects (ECOs). We encapsulate the absorbing properties of the analogue ECO by means of an effective boundary located around the analogue horizon. The presence of reflection at the effective boundary, characterised by a single parameter $\mathcal{K}$, allows for the existence of bound states located between the effective vortex core and the angular momentum barrier. The existence of these bound states leads to an enhanced absorption when the frequency of the incoming wave matches bound state frequencies, which result in Breit-Wigner type spectral lines in the absorption spectra. We also investigate the case of rotating analogue ECOs. In this scenario, some of the bound states undergo superradiant amplification and become unstable. In both the rotating and non-rotating case, we calculate numerically transmission/reflection spectra exhibiting the enhanced absorption/amplification. We complement our numerical study with WKB estimates as well as an extension of the Pöschl-Teller toy model which we solve analytically. Our simple model exhibits distinctive properties which could be observed in future analogue gravity experiments. We further argue that the observation of the spectral lines could be a way to characterise the effective field theory at play in the vicinity of the vortex core.

12 pages, 10 figures

References in corpus (5)

• Measurement of stimulated Hawking emission in an analogue system
• Instability of the massive Klein-Gordon field on the Kerr spacetime
• Self-Force Calculations with Matched Expansions and Quasinormal Mode Sums
• Quasi-normal frequencies: Key analytic results
• Rotating black holes in a draining bathtub: superradiant scattering of gravity waves

Cited by in corpus (5)

• Inverse problem of analog gravity systems
• On the origin of quasinormal modes in semi-open systems
• Vortices without inflow: bound spectra in horizonless rotational analogs
• Inverse problem of analog gravity systems II: Rotation and energy-dependent boundary conditions
• Bayesian analysis of analog gravity systems with the Rezzolla-Zhidenko metric