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  • Open Access

Limits on Global Cosmic Birefringence Using Radio Sources

Richard A. Battye*, Neal Jackson†, and Ian Browne‡

  • Jodrell Bank Centre for Astrophysics, Department of Physics and Astronomy, University of Manchester, Manchester, M13 9PL, United Kingdom

  • *Contact author: richard.battye@manchester.ac.uk
  • †Contact author: neal.jackson@manchester.ac.uk
  • ‡Contact author: ian.browne@manchester.ac.uk
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Phys. Rev. Lett. 137, 061001 – Published 3 August, 2026

DOI: https://doi.org/10.1103/5j64-ybm5

Abstract

We have made measurements of the difference between the position angle (PA) on the sky and the polarization position angle (PPA) of radio sources using data from a combination of the Radio Fundamental Catalogue (RFC) across a range of frequencies between 2.7 and 15 GHz and Cosmic Lens All-Sky Survey (CLASS) which observes polarization at 8.4 GHz (X-band). For the 2111 sources with jet PAs measured in the X-band and a known redshift, the distribution is peaked at ≈0° as expected for no birefringence and it can be modeled by two populations: one which is a Gaussian with mean μβ=(0.2±1.0)° and standard deviation σβ=(14.7±1.1)° and the other a uniform distribution of sources which are a fraction fβ=0.72±0.02 of the total. Uncertainties in μβ can be reduced to ≈0.6° by stacking measurements of the PA from other wavebands. We find that limits of ≈0.1° might be possible with a sample of ∼105 similarly selected sources and that this could provide a confirmation of recent claims of global birefringence made using the cosmic microwave background observations from the Planck satellite.

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Phys. Rev. Lett. 137, 061001– Published 3 August, 2026
  • Received 9 October 2025
  • Revised 2 March 2026
  • Accepted 22 June 2026
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