Scientists at the University of York have unveiled a pioneering theoretical framework that could fundamentally reshape how we approach the study of dark matter, the enigmatic entity that constitutes roughly 85% of the universe's total matter content. Historically, it has been a core tenet of cosmology that dark matter is entirely invisible to electromagnetic radiation because it neither absorbs, emits, nor reflects light. Its existence has been inferred solely through its powerful gravitational influence on the rotation of galaxies and the large-scale structure of the cosmos.
The new research, detailed in the journal Physics Letters B, posits a revolutionary hypothesis: light traversing regions dense with dark matter might acquire a barely perceptible spectral shift—a faint reddening or bluing. Researchers, including Dr. Mikhail Bashkanov, clarify that this is an indirect effect, utilizing the analogy of the “six degrees of separation” to illustrate the potential network of interactions. They suggest that the influence on photons could be mediated by intermediate Standard Model particles, such as the Higgs boson or the top quark, acting as temporary bridges between the visible and invisible sectors.
The precise nature of this spectral shift hinges critically on the composition of the dark matter itself. For instance, if dark matter is composed of Weakly Interacting Massive Particles (WIMPs), light might lose high-energy blue photons, resulting in a reddish hue. Conversely, if gravitational interaction dominates the process, the shift could lean toward the blue end of the spectrum. The wavelength shift predicted by this model is incredibly small, calculated to be in the range of $10^{-10}$ to $10^{-12}$. This magnitude is orders of magnitude below the sensitivity threshold of current spectrometers, meaning that verifying this audacious hypothesis demands a new generation of telescopes equipped with unparalleled spectral accuracy.
If this theory withstands experimental scrutiny, it would mark the first direct observational evidence of dark matter interacting, however subtly, with light, dramatically deepening our cosmic comprehension. This approach offers a powerful alternative to traditional methods. Instead of relying on the laborious and expensive search for particles in deep underground laboratories, scientists would gain the ability to analyze the spectra of light emanating from distant cosmic objects, pinpointing these subtle “color fingerprints” across vast cosmic distances. This theoretical breakthrough arrives while experimental investigations continue apace, providing crucial constraints on dark matter properties. For example, an international research team, utilizing the WINERED infrared spectrograph, established stringent constraints in February 2025 on the properties of dark matter particles with masses spanning 1.8 to 2.7 electronvolts. Crucially, however, no direct particle decay was observed during these high-precision measurements. This dual approach—combining theoretical prediction with high-precision empirical testing—is essential for finally solving the mystery of the universe's dominant, yet invisible, component.