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Binary supermassive black hole environments diminish the gravitational wave signal in the pulsar timing band

Ravi, V. and Wyithe, J. S. B. and Shannon, R. M. and Hobbs, G. and Manchester, R. N. (2014) Binary supermassive black hole environments diminish the gravitational wave signal in the pulsar timing band. Monthly Notices of the Royal Astronomical Society, 442 (1). pp. 56-68. ISSN 1365-2966. doi:10.1093/mnras/stu779.

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We assess the effects of supermassive black hole (SMBH) environments on the gravitational wave (GW) signal from binary SMBHs. To date, searches with pulsar timing arrays for GWs from binary SMBHs, in the frequency band ∼1–100 nHz, include the assumptions that all binaries are circular and evolve only through GW emission. However, dynamical studies have shown that the only way that binary SMBH orbits can decay to separations where GW emission dominates the evolution is through interactions with their environments. We augment an existing galaxy and SMBH formation and evolution model with calculations of binary SMBH evolution in stellar environments, accounting for non-zero binary eccentricities. We find that coupling between binaries and their environments causes the expected GW spectral energy distribution to be reduced with respect to the standard assumption of circular, GW-driven binaries, for frequencies up to ∼20 nHz. Larger eccentricities at binary formation further reduce the signal in this regime. We also find that GW bursts from individual eccentric binary SMBHs are unlikely to be detectable with current pulsar timing arrays. The uncertainties in these predictions are large, owing to observational uncertainty in SMBH–galaxy scaling relations and the galaxy stellar mass function, uncertainty in the nature of binary–environment coupling and uncertainty in the numbers of the most massive binary SMBHs. We conclude, however, that low-frequency GWs from binary SMBHs may be more difficult to detect with pulsar timing arrays than currently thought.

Item Type:Article
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URLURL TypeDescription Paper
Ravi, V.0000-0002-7252-5485
Additional Information:© 2014 The Authors. Published by Oxford University Press on behalf of the Royal Astronomical Society. Accepted 2014 April 17. Received 2014 April 17; in original form 2014 February 4. The authors thank Alberto Sesana, Sarah Burke-Spolaor, Yuri Levin, Simon Mutch, Paul Lasky and Jonathan Khoo for useful discussions. VR is a recipient of a John Stocker Postgraduate Scholarship from the Science and Industry Endowment Fund, and JSBW acknowledges an Australian Research Council Laureate Fellowship. The Millennium and Millennium-II simulation data bases used in this paper and the web application providing online access to them were constructed as part of the activities of the German Astrophysical Virtual Observatory. This work was performed on the swinSTAR supercomputer at the Swinburne University of Technology.
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Science and Industry Endowment FundUNSPECIFIED
Australian Research CouncilUNSPECIFIED
Subject Keywords:black hole physics, gravitational waves, methods: data analysis, galaxies: evolution
Issue or Number:1
Record Number:CaltechAUTHORS:20190626-101118264
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Official Citation:V. Ravi, J. S. B. Wyithe, R. M. Shannon, G. Hobbs, R. N. Manchester, Binary supermassive black hole environments diminish the gravitational wave signal in the pulsar timing band, Monthly Notices of the Royal Astronomical Society, Volume 442, Issue 1, 21 July 2014, Pages 56–68,
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:96724
Deposited By: George Porter
Deposited On:26 Jun 2019 19:48
Last Modified:16 Nov 2021 17:23

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