https://doi.org/10.1140/epjc/s10052-026-15479-5
Regular Article -Theoretical Physics
Quasibound states and superradiant instability of black hole in analog gravity
1
College of Physics and Materials Science, Tianjin Normal University, 300387, Tianjin, China
2
Particle Theory and Cosmology Group, Center for Theoretical Physics of the Universe, Institute for Basic Science (IBS), 34126, Daejeon, Republic of Korea
a
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Received:
17
December
2025
Accepted:
20
February
2026
Published online:
6
March
2026
Abstract
In this paper, we adopt continued fraction method (CFM) associated with VBK approach, which is recently developed by Vieira, Bezerra and Kokkotas, to investigate the spectrum of quasibound states (QBS) and superradiant instability of massive scalar perturbation imposed on analog rotating black hole in photon-fluid model. We analyze the effects of black hole angular velocity 
and scalar field mass 
on QBS spectrum with positive and negative winding number 
, respectively. In addition to the fundamental frequency, we also investigate the overtones in order to disclose more distinctions of spectrum between the states of . We show that the sign of winding number can produce notable impacts on the spectrum, particularly to the imaginary part of the spectrum. We study the superradiant instability and find that the maximum instability for a given is not in monotonic relationship with angular velocity, which is in contrast to the case in Kerr black hole spacetime. As expected, the strength of superradiant instability can be significantly weakened by increasing the winding number. These findings imply that there exists a critical angular velocity under which the instability is strongest in parameter space, and we are supposed to find it out at 
. Indeed, this max instability is found to be 
related to the critical angular velocity 
.
© The Author(s) 2026
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