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ABSTRACT Stars embedded in active galactic nucleus (AGN) discs or captured by them may scatter onto the supermassive black hole (SMBH), leading to a tidal disruption event (TDE). Using the moving-mesh hydrodynamics simulations with arepo, we investigate the dependence of debris properties in in-plane TDEs in AGN discs on the disc density and the orientation of stellar orbits relative to the disc gas (pro- and retro-grade). Key findings are: (1) Debris experiences continuous perturbations from the disc gas, which can result in significant and continuous changes in debris energy and angular momentum compared to ‘naked’ TDEs. (2) Above a critical density of a disc around an SMBH with mass M• [ρcrit ∼ 10−8 g cm−3 (M•/106 M⊙)−2.5] for retrograde stars, both bound and unbound debris is fully mixed into the disc. The density threshold for no bound debris return, inhibiting the accretion component of TDEs, is $$\rho _{\rm crit,bound} \sim 10^{-9}{\rm g~cm^{-3}}(M_{\bullet }/10^{6}\, {\rm M}_{\odot })^{-2.5}$$. (3) Observationally, AGN-TDEs transition from resembling naked TDEs in the limit of ρdisc ≲ 10−2ρcrit,bound to fully muffled TDEs with associated inner disc state changes at ρdisc ≳ ρcrit,bound, with a superposition of AGN + TDE in between. Stellar or remnant passages themselves can significantly perturb the inner disc. This can lead to an immediate X-ray signature and optically detectable inner disc state changes, potentially contributing to the changing-look AGN phenomenon. (4) Debris mixing can enrich the average disc metallicity over time if the star’s metallicity exceeds that of the disc gas. We point out that signatures of AGN-TDEs may be found in large AGN surveys. 

ABSTRACT It has been argued that heavy binaries composed of neutron stars (NSs) and millisecond pulsars (MSPs) can end up in the outskirts of star clusters via an interaction with a massive black hole (BH) binary expelling them from the core. We argue here, however, that this mechanism will rarely account for such observed objects. Only for primary masses ≲100 M⊙ and a narrow range of orbital separations should a BH–BH binary be both dynamically hard and produce a sufficiently low recoil velocity to retain the NS binary in the cluster. Hence, BH binaries are in general likely to eject NSs from clusters. We explore several alternative mechanisms that would cause NS/MSP binaries to be observed in the outskirts of their host clusters after a Hubble time. The most likely mechanism is a three-body interaction involving the NS/MSP binary and a normal star. We compare to Monte Carlo simulations of cluster evolution for the globular clusters NGC 6752 and 47 Tuc, and show that the models not only confirm that normal three-body interactions involving all stellar-mass objects are the dominant mechanism for putting NS/MSP binaries into the cluster outskirts, but also reproduce the observed NS/MSP binary radial distributions without needing to invoke the presence of a massive BH binary. Higher central densities and an episode of core collapse can broaden the radial distributions of NSs/MSPs and NS/MSP binaries due to three-body interactions, making these clusters more likely to host NSs in the cluster outskirts.