The primordial stars, known as group III, likely formed from the abundant gases present in the young universe. These stars were responsible for generating the first heavier elements, illuminating the universe, bringing an end to the cosmic dark ages, and ushering in the era of reionization. Due to the challenges of direct observation, the characteristics of these early stars are still largely unknown. Professor Anastasia Fialkov from Cambridge University and her team suggest that astronomers can infer the masses of these stars by analyzing the cosmological 21 cm signal produced by hydrogen atoms located between the regions where the stars formed.
Artist’s impression of a field of Population III stars that would have existed hundreds of millions of years post-Big Bang. Image credits: noirlab/nsf/aura/J. da silva/SpaceEngine.
“This presents a unique opportunity to understand how the universe’s first light emerged from darkness,” stated Professor Fialkov.
“We are beginning to unravel the narrative of the transition from a cold, dark cosmos to one filled with stars.”
Studies focused on the universe’s ancient stars rely on the faint 21 cm signal, an energy signature emanating from over 13 billion years ago.
This signal, influenced by the radiation from nascent stars and black holes, offers a rare glimpse into the universe’s formative years.
Professor Fialkov leads the Leach theory group dedicated to radio experiments analyzing space hydrogen.
“Leach is a radio antenna and one of two key projects designed to enhance our understanding of the dawn and reionization phases of the universe, when the first stars reactivated neutral hydrogen atoms,” explained the astronomer.
“While our abilities to capture radio signals are presently undergoing calibration, we remain dedicated to unveiling insights about the early universe.
“Conversely, the Square Kilometer Arrays (SKAs) chart variations in cosmic signals across extensive areas of the sky.”
“Both initiatives are crucial for probing the masses, brightness, and distribution of the universe’s earliest stars.”
In their current research, Professor Fialkov and co-authors formulated a model to predict the 21 cm signal for both REACH and SKA, discovering that the signal is sensitive to the mass of the first stars.
“We are the first group to accurately model how the 21 cm signal correlates with the mass of the first stars, factoring in ultraviolet starlight and x-ray emissions resulting from the demise of the first stars,” stated Professor Fialkov.
“Our findings stem from simulations integrating the primordial conditions of the universe, such as the hydrogen and helium composition formed during the Big Bang.”
In developing their theoretical framework, researchers examined how the 21 cm signal responds to the mass distribution of Population III stars.
They discovered that earlier studies underestimated this relationship as they failed to account for both the quantity and luminosity of x-ray binaries among Population III stars and their impact on the 21 cm signal.
While REACH and SKA cannot photograph individual stars, they do provide comprehensive data on stars, x-ray binary systems, and entire galactic populations.
“Connecting radio data to the narrative of the first stars requires some imagination, but its implications are profound,” remarked Professor Fialkov.
“The predictions we present hold significant value in enhancing our understanding of the universe’s earliest stars,” noted Dr. Eloi de Lera Acedo from Cambridge University.
“We offer insights into the masses of these early stars, suggesting that the light they emitted may have been drastically different from today’s stars.”
“Next-generation telescopes like REACH are set to unlock the secrets of the early universe. These predictions are vital for interpreting radio observations being conducted from Karu, South Africa.”
The research paper was published online today in the journal Nature Astronomy.
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T. Gessey-Jones et al. Determination of the mass distribution of the first stars from a 21 cm signal. Nature Astronomy Published online on June 20th, 2025. doi:10.1038/s41550-025-02575-x
Source: www.sci.news
