Astronomers Utilize Radio Signals to Identify First-Generation Stars

On June 20, 2025, a groundbreaking study published in *Nature Astronomy* revealed that astronomers are poised to glean insights into the Universe's first-generation stars, known as Population III stars, through the analysis of a unique cosmological radio signal. This signal, originating approximately 100 million years after the Big Bang, is created by hydrogen atoms that populate the gaps between early star-forming regions. The research team, led by Professor Anastasia Fialkov from the University of Cambridge, asserts that this discovery could illuminate how the Universe transitioned from darkness into a state filled with stars.

Historically, the formation of Population III stars has been enigmatic due to the lack of direct observations and the understanding of their characteristics, which are largely derived from theoretical models. These stars are considered crucial because they produced the first heavier elements and effectively ended the cosmic dark ages, initiating the Epoch of Reionization. Professor Fialkov emphasized the significance of this research, stating, "This is a unique opportunity to learn how the Universe’s first light emerged from the darkness."

The study focuses on the 21-cm signal, which is a faint glow that provides insights into the early Universe's conditions. This signal is influenced by the radiation emitted from early stars and black holes, which collectively offer a rare glimpse into the cosmic infancy. Fialkov's research group, which is part of the Radio Experiment for the Analysis of Cosmic Hydrogen (REACH), is currently calibrating its radio antenna aimed at capturing these signals. Alongside this initiative, the Square Kilometre Array (SKA) project aims to map fluctuations in cosmic signals across vast regions of the sky, which are vital for understanding the masses and distributions of the Universe’s earliest stars.

In their latest study, Fialkov and her colleagues developed a comprehensive model that predicts the behavior of the 21-cm signal from both REACH and SKA. This model notably accounts for the ultraviolet starlight and X-ray emissions generated by X-ray binaries that emerge following the death of the first stars. The researchers found that previous models had underestimated the relationship between the 21-cm signal and the masses of these ancient stars.

Dr. Eloy de Lera Acedo, also from the University of Cambridge and a co-author of the study, highlighted the profound implications of their findings: "The predictions we are reporting have huge implications for our understanding of the nature of the very first stars in the Universe."

The REACH and SKA projects will not be capable of imaging individual stars; however, they will provide essential information about entire populations of stars and galaxies. Both projects represent a significant advancement in astrophysical research, particularly in understanding the transition from a cold, dark Universe to one illuminated by the first stars. The research team underscored the importance of their work, explaining that while it may take imagination to connect radio data to the early Universe's story, the implications of their findings are profound.

The successful calibration and implementation of REACH, coupled with the expansive mapping capabilities of SKA, promise to unlock long-standing mysteries regarding the Universe's formative years. As these projects progress, they are expected to provide critical insights into the conditions that led to the formation of the first stars, thereby enhancing our understanding of cosmic history. The study serves as a pivotal step in the ongoing exploration of our Universe's origins, setting the stage for future discoveries in cosmology.