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Starfall: a heavy rain of stars in ‘turning on’ AGN

McKernan, B. and Ford, K. E. S. and Cantiello, M. and Graham, M. and Jermyn, A. S. and Leigh, N. W. C. and Ryu, T. and Stern, D. (2022) Starfall: a heavy rain of stars in ‘turning on’ AGN. Monthly Notices of the Royal Astronomical Society, 514 (3). pp. 4102-4110. ISSN 0035-8711. doi:10.1093/mnras/stac1310.

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As active galactic nuclei (AGN) ‘turn on’, some stars end up embedded in accretion discs around supermassive black holes (SMBHs) on retrograde orbits. Such stars experience strong headwinds, aerodynamic drag, ablation, and orbital evolution on short time-scales. The loss of orbital angular momentum in the first ∼0.1 Myr of an AGN leads to a heavy rain of stars (‘starfall’) into the inner disc and on to the SMBH. A large AGN loss cone (θ_(AGN, lc)) can result from binary scatterings in the inner disc and yield tidal disruption events (TDEs). Signatures of starfall include optical/UV flares that rise in luminosity over time, particularly in the inner disc. If the SMBH mass is M_(SMBH) ≳ 10⁸ M_⊙⁠, flares truncate abruptly and the star is swallowed. If M_(SMBH) < 10⁸ M_⊙⁠, and if the infalling orbit lies within θ_(AGN, lc), the flare is followed by a TDE that can be prograde or retrograde relative to the AGN inner disc. Retrograde AGN TDEs are overluminous and short-lived as in-plane ejecta collide with the inner disc and a lower AGN state follows. Prograde AGN TDEs add angular momentum to inner disc gas and so start off looking like regular TDEs but are followed by an AGN high state. Searches for such flare signatures test models of AGN ‘turn on’, SMBH mass, as well as disc properties and the embedded population.

Item Type:Article
Related URLs:
URLURL TypeDescription Paper
McKernan, B.0000-0002-9726-0508
Ford, K. E. S.0000-0002-5956-851X
Cantiello, M.0000-0002-8171-8596
Graham, M.0000-0002-3168-0139
Jermyn, A. S.0000-0001-5048-9973
Stern, D.0000-0003-2686-9241
Additional Information:© 2022 The Author(s) Published by Oxford University Press on behalf of Royal Astronomical Society. This article is published and distributed under the terms of the Oxford University Press, Standard Journals Publication Model ( Received: 07 October 2021. Revision received: 02 May 2022. Accepted: 03 May 2022. Published: 17 May 2022. Corrected and typeset: 29 June 2022. BM acknowledges very useful discussions with Wenbin Lu and Brian Metzger on some of the ideas that form the basis of this paper. BM and KESF are supported by NSF AST-1831415 and Simons Foundation Grant 533845. NWCL gratefully acknowledges the generous support of a Fondecyt Iniciación grant 11180005, as well as support from Millenium Nucleus NCN19-058 (TITANs) and funding via the BASAL Centro de Excelencia en Astrofisica y Tecnologias Afines (CATA) grant PFB-06/2007. NWCL also acknowledges support from ANID BASAL project ACE210002 and ANID BASAL projects ACE210002 and FB210003. The work of DS was carried out at the Jet Propulsion Laboratory, California Institute of Technology, under a contract with NASA. The Flatiron Institute is supported by the Simons Foundation. Thanks to Lucy Reading-Ikkanda for patiently assembling an excellent cartoon from our rough sketches. DATA AVAILABILITY. Any data used in this analysis are available on reasonable request from the first author (BM).
Funding AgencyGrant Number
Simons Foundation533845
Millennium Science InitiativeNCN19-058
Fondo Nacional de Desarrollo Científico y Tecnológico (FONDECYT)11180005
Agencia Nacional de Investigación y Desarrollo (ANID)ACE210002
Agencia Nacional de Investigación y Desarrollo (ANID)FB210003
Subject Keywords:accretion, accretion discs, black hole physics, gravitational waves, galaxies: active
Issue or Number:3
Record Number:CaltechAUTHORS:20220802-742608000
Persistent URL:
Official Citation:B McKernan, K E S Ford, M Cantiello, M Graham, A S Jermyn, N W C Leigh, T Ryu, D Stern, Starfall: a heavy rain of stars in ‘turning on’ AGN, Monthly Notices of the Royal Astronomical Society, Volume 514, Issue 3, August 2022, Pages 4102–4110,
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:116015
Deposited By: George Porter
Deposited On:02 Aug 2022 21:53
Last Modified:02 Aug 2022 21:53

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