Original title: Impact of uncertainties on the cosmic optical and infrared backgrounds on the propagation of astroparticles
Lucas Gréaux, Antonio Condorelli, Leonel Morejon, Karl-Heinz Kampert +1 · September 2026
As super-energetic particles travel across space, they collide with ambient cosmic light. Very-high-energy gamma rays, which are intense bursts of light above 100 GeV, and ultra-high-energy cosmic rays, which are speedy particles above 1 EeV, run into optical, infrared, and microwave photons. These collisions absorb gamma rays and alter the mass-compositionThe mix of different atomic nuclei in cosmic rays. of cosmic rays. Scientists struggled to analyze these traveling particles without knowing the exact brightness of this background light. In this study, researchers tested models of optical and infrared light that best match recent data to see how much lingering uncertainties affect particle journeys. They found that for nearby space at redshift z < 0.1, background light uncertainty is no longer the main problem. Future particle detectors can now produce dependable results.
Imagine trying to identify a bird by its silhouette against a hazy sky. The haze makes the shape unclear, so you cannot tell if it is a hawk or a crow, and you try different guesses about the haze thickness. In this paper, the haze corresponds to the uncertain glow that fills space between us and the source, and the bird corresponds to the astrophysical source. For nearby sources, the uncertainty in that glow no longer dominates.
For astronomers studying very-high-energy gamma rays and ultra-high-energy cosmic rays, the biggest unknown used to be the cosmic background light. This work shows that for nearby sources (within about 1.3 billion light-years), that uncertainty is no longer dominant. That means the next generation of telescopes and detectors can reliably infer the properties of these extreme sources, bringing us closer to understanding where cosmic rays come from.
The study only covers the low-redshift universe (z < 0.1); for more distant sources, background light uncertainties may still be significant. It also focuses on optical and infrared backgrounds, and relies on existing models that match recent measurements, so the conclusion depends on those measurements being correct.
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Impact of uncertainties on the cosmic optical and infrared backgrounds on the propagation of astroparticles — Lucas Gréaux, Antonio Condorelli, Leonel Morejon et al.
Abstract licence: CC0
Explanation generated by Synthesis from the abstract — it is not the original paper. This is a preprint, so it hasn't necessarily been peer reviewed.