In a discovery that could open a new window into one of physics’ greatest mysteries, researchers at Tel Aviv University have predicted what we might find by tuning into radio waves from the dawn of time. Their new study, led by Prof. Rennan Barkana of the Sackler School of Physics and Astronomy and published in the journal Nature Astronomy, suggests that dark matter formed “dense clumps” in the early universe, forcing hydrogen gas to emit a powerful, cumulative radio signal. This matters because it provides a theoretical roadmap for detecting dark matter not by seeing it, but by *listening* to its profound influence on the universe’s first atoms, offering a way to study it in its pristine, untouched state.
A window into the cosmic ‘dark ages’
Most of our news about the early universe comes from NASA’s James Webb Space Telescope, which is spotting the light from the first galaxies, roughly 300 million years after the Big Bang. This new research, however, pushes even further back into a more mysterious and earlier era: the “cosmic dark ages.” This period, just 100 million years after the Big Bang, was a time before a single star had formed. The universe was a dark, invisible soup of two main ingredients: hydrogen gas and the mysterious dark matter that we know makes up most of the matter in the cosmos.
How to detect the invisible
You can’t see dark matter directly. So, how do you study it? The researchers ran computer simulations to find its signature. They predict that during the dark ages, dark matter wasn’t spread out evenly. It gathered into dense clumps, or “nuggets,” whose size and shape depend on the unknown properties of dark matter itself. While these clumps are invisible, their gravity is not. They would have powerfully pulled in the abundant hydrogen gas that filled the universe. As this gas fell into the dark matter’s gravitational grip, it would have emitted intense radio waves. While any single clump’s signal is too faint, the team predicts that the “cumulative effect” of all these clumps would create a detectable “average radio intensity” across the entire sky. Listening to this signal could tell us about the clumps that created it, and thus, the nature of dark matter itself.
There’s a catch, of course. You can’t hear this ancient cosmic radio station from Earth. The specific radio waves from the dark ages are blocked by our planet’s atmosphere. To tune in, we’d need a radio telescope in space, and the best possible location is the moon. The lunar surface provides the perfect listening post: it has no atmosphere to block the signal and, just as importantly, it’s shielded from the constant, deafening roar of human-made radio interference from our own cell phones, Wi-Fi, and satellites. This idea, once pure science fiction, is suddenly plausible. A new global moon race is underway, with the U.S., Europe, China, and India all planning new lunar missions and actively seeking major scientific objectives for them.
The “cosmic dark ages” eventually ended with the “cosmic dawn,” when the first stars ignited. The light from these first stars dramatically amplified the original radio signal, making it much stronger. This louder, later signal is what massive new ground-based telescopes, like the Square Kilometre Array (SKA) in Australia, are being built to find.
The SKA, a global collaboration involving 80,000 antennas, will try to map this amplified signal to figure out where the first stars and dark matter clumps were. The trade-off is simple: the “cosmic dawn” signal is louder, but it’s also “harder to interpret,” as Prof. Barkana notes, because the stars themselves add their own complex noise. The “cosmic dark ages,” in contrast, are a “pristine laboratory”—the only one that will ever exist. It’s our one chance to study dark matter’s behavior in its original state, before the rest of the universe’s fireworks went off and “contaminated” the evidence.
