Skip to main content

Thank you for visiting nature.com. You are using a browser version with limited support for CSS. To obtain the best experience, we recommend you use a more up to date browser (or turn off compatibility mode in Internet Explorer). In the meantime, to ensure continued support, we are displaying the site without styles and JavaScript.

  • Year in Review
  • Published:

Highlights of 2023

Strong evidence for the discovery of a gravitational wave background

In 2023, pulsar timing arrays announced what could become the first ever discovery of a stochastic gravitational wave background: the random superposition of gravitational waves permeating the cosmos — a vestige of cosmic processes in the Universe. Upcoming datasets are expected to confirm the discovery and provide insight into the origin of this signal.

Key advances

  • Pulsar timing arrays worldwide have provided 2σ–4σ evidence for the detection of a gravitational wave signal in the form of a stochastic gravitational wave background consistent with astrophysical expectations.

  • By monitoring the deviations in the times of arrival of the radio frequency pulses of a large number of pulsars for many years it is possible to measure the gravitational redshift caused by gravitational waves emitted by far-away sources and travelling through spacetime between the pulsars and the Earth.

  • The signal can be explained in terms of the superposition of gravitational waves emitted by supermassive black hole binaries at the centre of galaxies; however, a more speculative origin, rooted in processes taking place in the very early Universe, for example at the quantum chromodynamics energy scale, is not excluded.

This is a preview of subscription content, access via your institution

Access options

Buy this article

Prices may be subject to local taxes which are calculated during checkout

Fig. 1: Evolution of the Universe and gravitational wave sources in the pulsar timing array frequency band.

References

  1. Agazie, G. et al. The NANOGrav 15 yr data set: evidence for a gravitational-wave background. Astrophys. J. Lett. 951, L8 (2023).

    Article  ADS  Google Scholar 

  2. Antoniadis, J. et al. The second data release from the European Pulsar Timing Array - III. Search for gravitational wave signals. Astron. Astrophys. 678, A50 (2023).

    Article  Google Scholar 

  3. Reardon, D. J. et al. Search for an isotropic gravitational-wave background with the Parkes Pulsar Timing Array. Astrophys. J. Lett. 951, L6 (2023).

    Article  ADS  Google Scholar 

  4. Xu, H. et al. Searching for the nano-hertz stochastic gravitational wave background with the Chinese Pulsar Timing Array data release I. Res. Astron. Astrophys. 23, 075024 (2023).

    Article  ADS  Google Scholar 

  5. Agazie, G. et al. Comparing recent PTA results on the nanohertz stochastic gravitational wave background. Preprint at https://doi.org/10.48550/arXiv.2309.00693 (2023).

  6. Arzoumanian, Z. et al. The NANOGrav 12.5 yr data set: search for an isotropic stochastic gravitational-wave background. Astrophys. J. Lett. 905, L34 (2020).

    Article  ADS  Google Scholar 

  7. Goncharov, B. et al. On the evidence for a common-spectrum process in the search for the nanohertz gravitational-wave background with the Parkes Pulsar Timing Array. Astrophys. J. Lett. 917, L19 (2021).

    Article  ADS  Google Scholar 

  8. Chen, S. et al. Common-red-signal analysis with 24-yr high-precision timing of the European Pulsar Timing Array: inferences in the stochastic gravitational-wave background search. Mon. Not. R. Astron. Soc. 508, 4970–4993 (2021).

    Article  ADS  Google Scholar 

  9. Agazie, G. et al. The NANOGrav 15 yr data set: constraints on supermassive black hole binaries from the gravitational-wave background. Astrophys. J. Lett. 952, L37 (2023).

    Article  ADS  Google Scholar 

  10. Antoniadis, J. et al. The second data release from the European Pulsar Timing Array: V. Implications for massive black holes, dark matter and the early Universe. Preprint at https://doi.org/10.48550/arXiv.2306.16227 (2023).

  11. Afzal, A. et al. The NANOGrav 15 yr data set: search for signals from new physics. Astrophys. J. Lett. 951, L11 (2023).

    Article  ADS  Google Scholar 

Download references

Author information

Authors and Affiliations

Authors

Corresponding author

Correspondence to Chiara Caprini.

Ethics declarations

Competing interests

The author declares no competing interests.

Rights and permissions

Reprints and permissions

About this article

Check for updates. Verify currency and authenticity via CrossMark

Cite this article

Caprini, C. Strong evidence for the discovery of a gravitational wave background. Nat Rev Phys 6, 291–293 (2024). https://doi.org/10.1038/s42254-024-00711-6

Download citation

  • Published:

  • Issue Date:

  • DOI: https://doi.org/10.1038/s42254-024-00711-6

Search

Quick links

Nature Briefing

Sign up for the Nature Briefing newsletter — what matters in science, free to your inbox daily.

Get the most important science stories of the day, free in your inbox. Sign up for Nature Briefing