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Gravitational-wave limits from pulsar timing constrain supermassive black hole evolution.

  • Author(s): Shannon, RM
  • Ravi, V
  • Coles, WA
  • Hobbs, G
  • Keith, MJ
  • Manchester, RN
  • Wyithe, JSB
  • Bailes, M
  • Bhat, NDR
  • Burke-Spolaor, S
  • Khoo, J
  • Levin, Y
  • Osłowski, S
  • Sarkissian, JM
  • van Straten, W
  • Verbiest, JPW
  • Wang, J-B
  • et al.

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)(H0/73 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.

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