Cosmic Metronome: Binary Stars Search for Axion Dark Matter

Original: "Reflection polarization of close binaries as a probe of axion dark matter birefringence"

· Tomoki Matsuoka, Kimihiro Nomura, Hidetoshi Omiya

arXiv:2607.04550v1 · 2026-07-05 · CC BY 4.0 · ⏱ 1 min · Cosmology Stellar HEP Phenomenology

Reflected polarization in close binary systems captures ultra-small oscillations of the polarization angle caused by axion birefringence, opening a window into the dark sector.

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The polarization of light from binary stars oscillates in sync with orbital motion, like a cosmic metronome. But if an invisible field of axions—dark matter—passes through this metronome, its hand will tremble almost imperceptibly, creating a silent accompaniment. Capturing this whisper means touching for the first time the substance that may make up a quarter of the Universe. And for that, you don't need giant accelerators—just look closely at the dance of light.

🎯 The polarization degree of Spica is just 0.02%—like spotting a candle through frosted glass from a kilometer away.

🎬 Using polarized light to detect elusive fields remotely echoes the attempts of the characters in Stanisław Lem's novel 'Solaris' to decipher signals from a sentient ocean. Only in our case, the 'ocean' is dark matter, and the 'signals' are microscopic oscillations of the polarization angle.

\theta_{a,0} = \frac{g_{a\gamma}}{2}\frac{\sqrt{2\rho}}{\mu}

θ_{a,0} is the amplitude of polarization angle oscillations, g_{aγ} is the axion-photon coupling constant, ρ is the dark matter density, μ is the axion mass.

f_{\text{signal}} = n f_{\text{orb}} \pm \mu

The sideband appears at a frequency shifted from the n-th harmonic of the orbital frequency by the axion mass μ.

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Cosmic Metronome: Binary Stars Search for Axion Dark Matter