Galactic microlensing by acoustic Schwarzschild black holes

Abstract This work explores the application of acoustic black holes as a novel class of lenses in Galactic microlensing, potentially representing dark matter halo objects. While sharing key features like an event horizon, their underlying fluid-dynamical description differs from the vacuum solutions of Einstein’s equations, suggesting potentially distinct observational signatures. This work investigates these distinctions by calculating the galactic microlensing predictions for acoustic black holes and comparing them to the standard Schwarzschild case. Using the observed parameters of known black hole candidates (Cygnus X-1, A0620-00, GRO J1655-40) as illustrative lenses, we demonstrate that the acoustic black holes tuning parameter $$\xi $$ ξ significantly alters key observables. Our results show that an increase in $$\xi $$ ξ leads to a larger Einstein ring radius, a longer event duration, and a higher peak magnification in the microlensing Paczyński light curves. Furthermore, we find that the microlensing event rate is enhanced for acoustic black holes compared to their Schwarzschild counterparts, with the probability of detection growing with $$\xi $$ ξ . These findings establish galactic microlensing as a promising astrophysical channel for constraining analogue gravity metrics, with the primary effects being potentially detectable in the statistical analysis of current and future microlensing survey data.