Nanohertz Gravitational-Wave Constraints on Supermassive Binary Black Holes at Cosmic Dawn

PPTA Collaboration; Yiqin Chen; Shi-Yi Zhao; Xingjiang Zhu; N. D. Ramesh Bhat; Jacob Cardinal Tremblay; Małgorzata Curyło; Valentina Di Marco; George Hobbs; Wenhua Ling; Rami F. Mandow; Richard N. Manchester; Saurav Mishra; Daniel J. Reardon; Sparrow Roch; Christopher J. Russell; Ryan M. Shannon; Jingbo Wang; Shuangqiang Wang; Andrew Zic

doi:10.1103/5z5g-shly

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Nanohertz Gravitational-Wave Constraints on Supermassive Binary Black Holes at Cosmic Dawn

Yiqin Chen^1,2,*, Shi-Yi Zhao^1,2,*, Xingjiang Zhu ^1,†, N. D. Ramesh Bhat³, Jacob Cardinal Tremblay^4,5, Małgorzata Curyło^6,7, Valentina Di Marco^8,7, George Hobbs⁹, Wenhua Ling⁹ et al. (PPTA Collaboration)

Wenhua Ling⁹, Rami F. Mandow^10,9, Richard N. Manchester⁹, Saurav Mishra¹¹, Daniel J. Reardon^11,7, Sparrow Roch^11,7, Christopher J. Russell¹², Ryan M. Shannon^11,7, Jingbo Wang¹³, Shuangqiang Wang^14,9, and Andrew Zic^9,7 (PPTA Collaboration)

¹Institute for Frontiers in Astronomy and Astrophysics and Faculty of Arts and Sciences, Beijing Normal University, Zhuhai 519087, China
²School of Physics and Astronomy, Beijing Normal University, Beijing 100875, China
³International Centre for Radio Astronomy Research, Curtin University, Bentley, Western Australia 6102, Australia
⁴Max Planck Institute for Gravitational Physics (Albert Einstein Institute), 30167 Hannover, Germany
⁵Leibniz Universität Hannover, 30167 Hannover, Germany
⁶School of Physics and Astronomy, Monash University, Clayton, Victoria 3800, Australia
⁷ ARC Centre of Excellence for Gravitational Wave Discovery (OzGrav)
⁸School of Physics, University of Melbourne, Parkville, Victoria 3010, Australia
⁹Australia Telescope National Facility, CSIRO Space and Astronomy, PO Box 76, Epping, New South Wales 1710, Australia
¹⁰Department of Mathematics and Physical Sciences, Macquarie University, Sydney, New South Wales 2109, Australia
¹¹Centre for Astrophysics and Supercomputing, Swinburne University of Technology, Hawthorn, Victoria 3122, Australia
¹²CSIRO Scientific Computing, PO Box 76, Epping, New South Wales 1710, Australia
¹³Institute of Optoelectronic Technology, Lishui University, Lishui 323000, China
¹⁴Xinjiang Astronomical Observatory, Chinese Academy of Sciences, Urumqi, Xinjiang 830011, China

^*These authors contributed equally to this work.
^†Contact author: zhuxj@bnu.edu.cn

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Phys. Rev. Lett. 137, 191401 – Published 2 November, 2026

DOI: https://doi.org/10.1103/5z5g-shly

Abstract

Standard continuous gravitational-wave searches with pulsar timing arrays (PTAs) neglect cosmological redshift, restricting their applicability to the local Universe. We introduce a redshift-aware PTA framework and apply it to the Parkes PTA Data Release 3, deriving the first direct constraints on supermassive binary black holes (SMBBHs) at the cosmic dawn. Evaluating our limits across a broad redshift range, we observationally establish the nonmonotonic mass-redshift exclusion boundary driven by the theoretical “redshift bias,” demonstrating how PTAs can effectively probe sources at extreme distances. Redshift-aware targeted searches toward high-redshift systems, including the ultraluminous quasar $J 0100 + 2802$ ( $z = 6.327$ ) and the JWST-discovered galaxy JADES-GS-z14-0 ( $z = 14.32$ ), rigorously exclude SMBBHs with chirp masses $M_{c} ≳ 10^{10} M_{⊙}$ across the nanohertz frequency band. Finally, we demonstrate that high-redshift binaries can be robustly detected and localized, allowing for the accurate measurement of their intrinsic properties. Our results provide the tightest constraints to date on SMBBHs at $z > 6$ and establish a practical framework for probing early-Universe black hole assembly.

Physical Review Letters

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