The Magnified Waltz: Simulating Light Curves of Binary Stars Passing Through Microcaustics in Strong Lensing Galaxy Clusters

Abstract Individual stars located near the caustics of galaxy clusters can undergo extreme magnification when crossing microcaustics, rendering them observable even at cosmological distances. Though most massive stars are likely to reside in binary systems rather than as single star, the influence of a binary star system on magnification events is severely underexplored. In this work, we simulate the light curves produced by detached binary stars crossing microcaustics, aiming to characterize their unique observational signatures. Using high-resolution magnification maps generated by the GPU-PMO-CAUSTIC algorithm and PARSEC stellar models with red-shifted magnitude, we examined the impact of binary star parameters and crossing geometries on microlensing magnification patterns. Our simulations reveal that binary stars produce diverse light-curve features, including overlapping peaks, plateau-like structures, and time-variable color–magnitude differences. These features, particularly the distinct temporal variations in spectral energy distributions, offer diagnostic tools for distinguishing binary systems from single stars. We further demonstrate the potential of multiband photometry using the Chinese Space Station Telescope’s Multi-Channel Imager to capture these variations. Our findings provide theoretical support to identify binary systems in future caustic-crossing events, enabling more accurate characterization of high-redshift stellar populations.