New constraints on the values of the fundamental constants at a look-back time of 7.3 Gyr

¹ Shanghai Astronomical Observatory, Chinese Academy of Sciences, 80 Nandan Road, Shanghai 200030, China
² Research Center for Astronomical Computing, Zhejiang Laboratory, Hangzhou 311100, China
³ School of Chemical and Physical Sciences, Victoria University of Wellington, PO Box 600, Wellington 6140, New Zealand
⁴ Observatoire de Paris, LERMA, Collège de France, CNRS, PSL University, Sorbonne University, 75014, Paris, France
⁵ Inter-University Centre for Astronomy and Astrophysics, Post Bag 4, Ganeshkhind, Pune, 411 007, India
⁶ Department of Space, Earth and Environment, Chalmers University of Technology, Onsala Space Observatory, 43992 Onsala, Sweden
⁷ New Cornerstone Science Laboratory, Department of Astronomy, Tsinghua University, Beijing 100084, China
⁸ National Astronomical Observatories, Chinese Academy of Sciences, Beijing 100012, China

^⋆ Corresponding author: rzsu.astro@gmail.com

Received: 12 December 2024
Accepted: 9 May 2025

Abstract

The study of redshifted spectral lines can provide a measure of the fundamental constants over large look-back times. Current grand unified theories predict an evolution in these constants and astronomical observations offer the only experimental measure of the values of the constants over large timescales. Of particular interest are the dimensionless constants: the fine structure constant (α), the proton-electron mass ratio (μ), and the proton g-factor (g_p), since these do not require a “standard meterstick”. Here we present a re-analysis of the 18 cm hydroxyl (OH) lines at z = 0.89, which were recently detected with the MeerKAT telescope, toward the radio source PKS 1830-211. Utilizing the previous constraint of Δμ/μ=(−1.8±1.2)×10⁻⁷, we obtain Δ(α g_p^0.27)/(α g_p^0.27) ≲ 5.7 × 10⁻⁵, Δα/α≲2.3×10⁻³, and Δg_p/g_p≲7.9×10⁻³. These new constraints are consistent with no evolution over a look-back time of 7.3 Gyr and provide another valuable data point in the putative evolution of the constants.