In-plane tidal disruption of stars in discs of active galactic nuclei

Author:

Ryu Taeho12ORCID,McKernan Barry3456ORCID,Ford K E Saavik3456ORCID,Cantiello Matteo3,Graham Matthew7ORCID,Stern Daniel8,Leigh Nathan W C49

Affiliation:

1. Max Planck Institute for Astrophysics , Karl-Schwarzschild-Str. 1, D-85748 Garching , Germany

2. Physics and Astronomy Department, Johns Hopkins University , Baltimore, MD 21218 , USA

3. Center for Computational Astrophysics, Flatiron Institute , New York, NY 10010 , USA

4. Department of Astrophysics, American Museum of Natural History , New York, NY 10024 , USA

5. Graduate Center, City University of New York , 365 5th Avenue, New York, NY 10016 , USA

6. Department of Science, BMCC, City University of New York , New York, NY 10007 , USA

7. California Institute of Technology , 1200 E. California Blvd, Pasadena, CA 91125 , USA

8. Jet Propulsion Laboratory, California Institute of Technology , 4800 Oak Grove Drive, Pasadena, CA 91109 , USA

9. Departamento de Astronomá, Facultad de Ciencias Fśicas y Matemáticas, Universidad de Concepción , 4070409 Concepción , Chile

Abstract

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.

Funder

Friedrich-Alexander-Universität Erlangen-Nürnberg

FAU

German Research Foundation

DFG

NSF

Simons Foundation

NCN

CATA

Publisher

Oxford University Press (OUP)

Subject

Space and Planetary Science,Astronomy and Astrophysics

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