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 with 95% confidence to be ΩGW(H0/73kms−1Mpc−1)2<1.3×10−9 at a frequency of 2.8 nHz, which is approximately a factor of six 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 simulations is inconsistent with our limit with 50% probability.
@article{arxiv.1310.4569,
title = {Gravitational-wave Limits from Pulsar Timing Constrain Supermassive Black Hole Evolution},
author = {R. M. Shannon and V. Ravi and W. A. Coles and G. Hobbs and M. J. Keith and R. N. Manchester and J. S. B. Wyithe and M. Bailes and N. D. R. Bhat and S. Burke-Spolaor and J. Khoo and Y. Levin and S. Osłowski and J. M. Sarkissian and W. van Straten and J. P. W. Verbiest and J-B. Wang},
journal= {arXiv preprint arXiv:1310.4569},
year = {2015}
}