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    Hydrodynamic simulations of tidal disruption encores

    Ian P. A. Johnson1,*, Taeho Ryu2,3,4, and Rosalba Perna1

    • *Contact author: ian.p.johnson@stonybrook.edu

    Phys. Rev. D 113, 043032 – Published 17 February, 2026

    DOI: https://doi.org/10.1103/3g9b-967g

    Abstract

    We present hydrodynamic simulations with the moving-mesh code arepo of tidal disruption encores (TDEEs) in nuclear star clusters (NSCs). TDEEs arise when a stellar-mass black hole (sBH) disrupts a star within the NSC, producing debris that is unbound from the sBH but remains gravitationally bound to the central massive black hole (MBH), leading to a delayed secondary flare. We find that the morphology and thermodynamics of the fallback material depend sensitively on the disruption geometry, MBH mass, and sBH-MBH separation. We identify two distinct morphological outcomes: ring encores, where debris circularize into a torus, and direct encores, where streams plunge toward the MBH, with encore luminosities peaking at times corresponding to the freefall timescale and one orbital period, respectively. Across all simulated cases, we find these events exhibit luminosities of 1040–1042  erg/s with lightcurves characteristic of their morphology. Our work greatly improves the predictions of TDEE lightcurves and empowers observations to probe into NSC dynamics and sBH population while providing possible explanations for anomalous TDE-like flares.

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