Gravitational-Wave Limits from Pulsar Timing Constrain Supermassive Black Hole Evolution

Creators: Shannon, R. M.; Ravi, V.; Coles, W. A.; Hobbs, G.; Keith, M. J.; Manchester, R. N.; Wyithe, J. S. B.; Bailes, M.; Bhat, N. D. R.; Burke-Spolaor, S.; Khoo, J.; Levin, Y.; Oslowski, S.; Sarkissian, J. M.; van Straten, W.; Verbiest, J. P. W.; Wang, J.-B.

Abstract

The formation and growth processes of supermassive black holes (SMBHs) are not well constrained. SMBH population models, however, provide specific predictions for the properties of the gravitational-wave background (GWB) from binary SMBHs in merging galaxies throughout the universe. Using observations from the Parkes Pulsar Timing Array, we constrain the fractional GWB energy density (Ω_(GW)) with 95% confidence to be Ω_(GW)(H_0/73 kilometers per second per megaparsec)^2 < 1.3 × 10^(−9) (where H0 is the Hubble constant) at a frequency of 2.8 nanohertz, which is approximately a factor of 6 more stringent than previous limits. We compare our limit to models of the SMBH population and find inconsistencies at confidence levels between 46 and 91%. For example, the standard galaxy formation model implemented in the Millennium Simulation Project is inconsistent with our limit with 50% probability.

Additional Information

© 2013 American Association for the Advancement of Science. 19 March 2013; accepted 6 September 2013. We thank all of the observers, engineers, and Parkes observatory staff members who have assisted with the observations reported in this paper. We thank N. McConnell for providing and confirming some dynamical SMBH and bulge mass measurements, S. Mutch for discussions on the Millennium-based model, and X.-J. Zhu for comments on the manuscript. The Parkes radio telescope is part of the Australia Telescope National Facility, which is funded by the Commonwealth of Australia for operation as a National Facility managed by CSIRO. The Millennium and Millennium-II Simulation databases used in this paper and the Web application providing online access to these databases were constructed as part of the activities of the German Astrophysical Virtual Observatory. The PPTA project was initiated with support from R.N.M.'s Australian Research Council (ARC) Federation Fellowship (no. FF0348478) and from the CSIRO under that fellowship program. The PPTA project has also received support from ARC Discovery Project grant no. DP0985272. V.R. is a recipient of a John Stocker Postgraduate Scholarship from the Science and Industry Endowment Fund, G.H. is the recipient of an ARC QEII Fellowship (no. DP0878388), and J.S.B.W. acknowledges an Australian Research Council Laureate Fellowship. Part of this research was carried out at the Jet Propulsion Laboratory, California Institute of Technology, under a contract with NASA. J.P.W.V. acknowledges the financial support by the European Research Council (ERC) for the ERC Starting Grant Beacon under contract no. 279202. The authors declare no conflicts of interest. Data used in this analysis can be accessed via the Australia National Data Service (www.ands.org.au).

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