Reading signatures of supermassive binary black holes in pulsar timing array observations

Boris Goncharov (), Shubhit Sardana, Alberto Sesana, Sharon Mary Tomson, John Antoniadis, Aurelien Chalumeau, David J. Champion, Siyuan Chen, Evan F. Keane, Kuo Liu, Golam Shaifullah, Lorenzo Speri and Serena Valtolina
Additional contact information
Boris Goncharov: Max Planck Institute for Gravitational Physics (Albert Einstein Institute)
Shubhit Sardana: Max Planck Institute for Gravitational Physics (Albert Einstein Institute)
Alberto Sesana: Universitá degli Studi di Milano-Bicocca
Sharon Mary Tomson: Max Planck Institute for Gravitational Physics (Albert Einstein Institute)
John Antoniadis: N. Plastira 100
Aurelien Chalumeau: Netherlands Institute for Radio Astronomy
David J. Champion: Max-Planck-Institut für Radioastronomie
Siyuan Chen: Chinese Academy of Sciences
Evan F. Keane: College Green
Kuo Liu: Chinese Academy of Sciences
Golam Shaifullah: Universitá degli Studi di Milano-Bicocca
Lorenzo Speri: Max Planck Institute for Gravitational Physics (Albert Einstein Institute)
Serena Valtolina: Max Planck Institute for Gravitational Physics (Albert Einstein Institute)

Nature Communications, 2025, vol. 16, issue 1, 1-8

Abstract: Abstract Constraining the origin of the nanohertz gravitational-wave background necessitates precise noise modelling to avoid parameter estimation biases. In this work, we find the inferred properties of the putative gravitational wave background in the second data release of the European Pulsar Timing Array to be in better agreement with theoretical expectations under the improved noise model. In particular, our improved noise models show consistency of the background’s strain spectral index with the value of −2/3, favoring the population of supermassive black hole binaries as the origin of the background. Our results further suggest that the observed gravitational wave emission is the dominant source of the binary energy loss, with no evidence of environmental effects or eccentric orbits. At the reference gravitational wave frequency of yr−1, we also find a lower power-law strain amplitude of the background than in previous data analyses. This mitigates some of the tensions of the strain amplitude with the expected number density and mass scale of binaries discussed in the literature. Our analysis demonstrates the importance of accurate modelling of radio pulsar pulse profile variations, hierarchical properties of noise across pulsars, as well as noise model averaging, when inferring properties of the gravitational wave background.

Date: 2025
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DOI: 10.1038/s41467-025-65450-3

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