Understanding the transition of the universe from darkness to light, marked by the formation of the first stars and galaxies, remains a significant challenge in astronomy. Direct observation of these earliest stars is not possible even with advanced telescopes. However, an international team led by the University of Cambridge has identified a method to learn about these early stars' masses through a specific radio signal.
The researchers focused on a radio signal created by hydrogen atoms that emerged approximately 100 million years after the Big Bang. This signal, known as the 21-centimetre signal, provides insights into how early stars and their remnants influenced it. The study suggests that future radio telescopes will enhance our understanding of how the universe evolved from a nearly uniform mass to its current complexity. These findings are published in Nature Astronomy.
Professor Anastasia Fialkov from Cambridge’s Institute of Astronomy commented on this opportunity: “This is a unique opportunity to learn how the universe’s first light emerged from the darkness.” She highlighted that understanding this transition is still in its infancy.
The research focuses on studying faint signals emitted over 13 billion years ago, which offer rare insights into early cosmic conditions. Fialkov leads REACH (the Radio Experiment for the Analysis of Cosmic Hydrogen), one of two major projects aimed at exploring this era alongside SKA (Square Kilometre Array).
Although REACH is currently being calibrated, it promises valuable data about the early universe. Meanwhile, SKA will map cosmic signals across large sky regions. Both projects are crucial for examining characteristics like mass and luminosity of early stars.
Fialkov noted: “We are the first group to consistently model the dependence of the 21-centimetre signal on the masses of first stars,” emphasizing insights gained from simulations based on primordial conditions.
Their model considers how X-ray binaries among Population III stars affect this signal—a factor previous studies underestimated due to not accounting for such systems' numbers and brightness.
Radio astronomy relies heavily on statistical analysis rather than imaging individual objects. REACH and SKA will provide information about entire star populations instead.
Dr Eloy de Lera Acedo remarked: “The predictions we are reporting have huge implications for our understanding," indicating potential revelations about differences between ancient and modern stars.
These efforts receive support partly from UK Research and Innovation's Science and Technology Facilities Council (STFC). Professor Fialkov holds fellowships at Magdalene College while Dr de Lera Acedo is affiliated with Selwyn College under an STFC Ernest Rutherford Fellowship.
Reference:
T. Gessey-Jones et al., ‘Determination of mass distribution...’ Nature Astronomy (2024). DOI: 10.1038/s41550-025-02575-x