Dark matter—the mysterious substance that makes up about 27% of the universe—has long been thought to be completely invisible. But new research suggests that it might not be as dark as we think.
Scientists at the University of York have found that dark matter could leave a faint “fingerprint” on light as it travels through space, potentially appearing as a tiny red or blue tint.
The study, published in Physics Letters B, challenges one of the most deeply held assumptions in physics—that dark matter and light never interact.
Until now, scientists have only detected dark matter through its gravitational effects.
It doesn’t emit, reflect, or absorb light, but its invisible pull holds galaxies together and shapes the large-scale structure of the universe.
The York researchers, however, propose that the story might be more complicated. Their theoretical work suggests that light passing through regions filled with dark matter could be subtly altered, shifting slightly toward the red or blue end of the spectrum depending on the properties of the dark matter it encounters.
Dr. Mikhail Bashkanov from the University of York’s School of Physics, Engineering and Technology compared the process to the “six handshake rule” — the idea that any two people on Earth are connected through a short chain of acquaintances.
He explained that even if dark matter doesn’t directly interact with light, it might still influence it indirectly through a series of intermediate particles.
For instance, one popular dark matter candidate, known as a WIMP (Weakly Interacting Massive Particle), might affect light by interacting with particles such as the Higgs boson or the top quark, which in turn interact with photons—the particles of light. Through this chain of connections, light could pick up a tiny color signature, a kind of “cosmic tint,” as it passes through dark matter.
“It’s a fascinating idea,” Dr. Bashkanov said. “Most scientists assume that dark matter is completely dark. But our research shows that even the darkest kind imaginable could still have a faint color signature—and under the right conditions, that signature might actually be detectable.”
He added that with the next generation of advanced telescopes, astronomers could look for this subtle fingerprint in the light coming from distant stars and galaxies. If detected, it could provide a new and simpler way to study dark matter without relying solely on massive underground detectors or particle accelerators.
The findings could also help scientists narrow down which types of dark matter are most likely to exist, allowing them to rule out some theories and focus on others.
“We’re spending billions on experiments to find WIMPs, axions, or dark photons,” Bashkanov noted. “Our results could help focus those searches and show where in the sky we should be looking.”
If confirmed, this discovery could transform how we study one of the universe’s greatest mysteries—shedding a little light on the dark side of the cosmos.
