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Tidal disruption events from supermassive black hole binaries

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journal contribution
posted on 04.01.2017, 14:52 by E. R. Coughlin, P. J. Armitage, Chris Nixon, M. C. Begelman
We investigate the pre-disruption gravitational dynamics and post-disruption hydrodynamics of the tidal disruption of stars by supermassive black hole (SMBH) binaries. We focus on binaries with relatively low mass primaries (106 M⊙), moderate mass ratios, and separations with reasonably long gravitational wave inspiral times (tens of Myr). First, we generate a large ensemble (between 1 and 10 million) of restricted three-body integrations to quantify the statistical properties of tidal disruptions by circular SMBH binaries of initially unbound stars. Compared to the reference case of a disruption by a single SMBH, the binary potential induces a significant variance into the specific energy and angular momentum of the star at the point of disruption. Second, we use Newtonian numerical hydrodynamics to study the detailed evolution of the fallback debris from 120 disruptions randomly selected from the three-body ensemble (excluding only the most deeply penetrating encounters). We find that the overall morphology of the debris is greatly altered by the presence of the second black hole, and the accretion rate histories display a wide range of behaviours, including order of magnitude dips and excesses relative to control simulations that include only one black hole. Complex evolution typically persists for many orbital periods of the binary. We find evidence for power in the accretion curves on time-scales related to the binary orbital period, though there is no exact periodicity. We discuss our results in the context of future wide-field surveys, and comment on the prospects of identifying and characterizing the subset of events occurring in nuclei with binary SMBHs.

Funding

Support for this work was provided by NASA through the Einstein Fellowship Program, grant PF6-170150, NSF grants AST 1313021 and 1411879, and NASA grants NNX14AB42G and NNX16AI40G. CN was supported by the Science and Technology Facilities Council (STFC; grant number ST/M005917/1). Research in theoretical astrophysics at Leicester is supported by an STFC Consolidated Grant. This work utilized the Janus supercomputer, which is supported by the National Science Foundation (award number CNS-0821794) and the University of Colorado Boulder. The Janus supercomputer is a joint effort of the University of Colorado Boulder, the University of Colorado Denver, and the National Center for Atmospheric Research.

History

Citation

Monthly Notices of the Royal Astronomical Society, 2016, 465 (4), pp. 3840-3864

Author affiliation

/Organisation/COLLEGE OF SCIENCE AND ENGINEERING/Department of Physics and Astronomy

Version

VoR (Version of Record)

Published in

Monthly Notices of the Royal Astronomical Society

Publisher

Oxford University Press (OUP), Royal Astronomical Society

issn

0035-8711

eissn

1365-2966

Acceptance date

07/11/2016

Available date

04/01/2017

Publisher version

http://mnras.oxfordjournals.org/content/465/4/3840

Language

en

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