For the first time, researchers at Tel Aviv University have predicted what might be discovered by detecting radio waves that originated in the early Universe. Their results suggest that during the “cosmic dark ages,” dark matter gathered into dense clumps across space, pulling in hydrogen gas that emitted intense radio waves. This new approach could offer a way to investigate one of science’s biggest mysteries: the true nature of dark matter.
The work, led by Prof. Rennan Barkana from Tel Aviv University’s Sackler School of Physics and Astronomy, involved Ph.D. student Sudipta Sikder and collaborators from Japan, India, and the United Kingdom. Their findings were published in Nature Astronomy.
Studying the Cosmic Dark Ages from the Moon
According to the researchers, the cosmic dark ages (the period just before the first stars formed) can be explored by detecting radio waves emitted by the hydrogen gas that once filled the Universe. Although everyday antennas easily detect radio waves, the signals from this ancient era are blocked by Earth’s atmosphere. Studying them requires instruments in space — especially on the moon, where the lack of an atmosphere and human-made interference provides ideal conditions.
Building a telescope on the lunar surface is a formidable task, but the timing may be right. A global race is underway to return to the moon, with the United States, Europe, China, and India all pursuing new lunar missions. These agencies are seeking meaningful scientific objectives for future moon projects, and this new research underscores the potential of lunar-based radio astronomy to probe the early Universe.
Exploring the Universe Before the First Stars
Prof. Barkana explains: “NASA’s new James Webb space telescope discovered recently distant galaxies whose light we receive from early galaxies, around 300 million years after the Big Bang. Our new research studies an even earlier and more mysterious era: the cosmic dark ages, only 100 million years after the Big Bang. Computer simulations predict that dark matter throughout the Universe was forming dense clumps, which would later help form the first stars and galaxies. The predicted size of these nuggets depends on, and thus can help illuminate, the unknown properties of dark matter, but they cannot be seen directly. However, these dark matter clumps pulled in hydrogen gas and caused it to emit stronger radio waves. We predict that the cumulative effect of all this can be detected with radio antennas that measure the average radio intensity on the sky.”
These simulations suggest that radio signals from the dark ages, while faint, carry valuable clues about the invisible structures that seeded the formation of galaxies. Detecting them could transform our understanding of the Universe’s earliest moments.
From the Cosmic Dark Ages to the Dawn of Stars
Although the expected signal is weak, successfully observing it could open a new window for testing theories of dark matter. When the first stars appeared shortly afterward, during a phase known as the “cosmic dawn,” their light likely amplified this radio emission dramatically. Signals from that later era should be easier to detect with ground-based telescopes, though they are harder to interpret because star formation introduces additional complexity.
To tackle this challenge, scientists are turning to vast radio telescope networks designed to map subtle variations in cosmic radio intensity. One of the largest efforts is the Square Kilometre Array (SKA), a global collaboration involving an array of 80,000 radio antennas currently under construction in Australia. Prof. Barkana plays a key role in this international project, which aims to capture patterns of strong and weak radio emissions that could reveal where dark matter clumps once existed.
A New Window Into Dark Matter’s Origins
The team believes that their predictions may provide an important step forward in understanding dark matter. Today, dark matter is intertwined with galaxies and stars, making its properties difficult to isolate. In contrast, the early Universe offers a pristine setting — essentially an untouched laboratory — for investigating how dark matter behaves without interference from later cosmic structures.
Prof. Barkana concludes: “Just as old radio stations are being replaced with newer technology that brings forth websites and podcasts, astronomers are expanding the reach of radio astronomy. When scientists open a new observational window, surprising discoveries usually result. The holy grail of physics is to discover the properties of dark matter, the mysterious substance that we know constitutes most of the matter in the Universe, yet we do not know much about its nature and properties. Understandably, astronomers are eager to start tuning into the cosmic radio channels of the early Universe.”
