Jerusalem, 19 October, 2025 (TPS-IL) — A groundbreaking Israeli-led international study revealed that most massive stars in the early universe were born as binary systems, shedding new light on the origins of the cosmos and the processes that shaped it. The research, announced by Tel Aviv University, suggests that, like their counterparts in the Milky Way today, massive stars frequently formed in pairs, fundamentally influencing galaxy evolution, the formation of black holes, and the distribution of elements essential for life.
The study, led by Dr. Tomer Shenar of the School of Physics and Astronomy at Tel Aviv University, alongside Dr. Hugues Sana of KU Leuven University in Belgium and Dr. Julia Bodensteiner of the University of Amsterdam in the Netherlands, was published in the peer-reviewed journal Nature Astronomy.
“Massive stars, those with at least ten times the mass of the Sun, are responsible for a variety of cosmic phenomena,” Shenar explained. “A single massive star can emit more energy than a million Sun-like stars. They shape the structure and properties of their host galaxies, produce most of the universe’s heavy elements, and end their lives in powerful supernova explosions, leaving behind neutron stars and black holes.”
In the Milky Way, astronomers have long known that most massive stars are born in “binary systems,” pairs so close that they often exchange matter and sometimes merge. These interactions drastically alter the stars’ evolution and ultimate fate. Until now, it remained unclear whether this pattern of binarity also applied to the first massive stars that formed in the early universe.
Observing these ancient stars directly is difficult because the earliest galaxies lie billions of light-years away. To overcome this challenge, Dr. Shenar and his team designed an observational survey targeting massive stars in a nearby galaxy with conditions similar to the early universe. “As part of the survey Binarity at LOw Metallicity (BLOeM), we carried out a two-year observing campaign with the VLT in Chile, during which we obtained spectra of about 1,000 massive stars in the Small Magellanic Cloud—a neighboring galaxy with a low metal content, resembling the composition of the young universe,” Dr. Shenar said.
By analyzing the stars’ spectra, the researchers detected periodic motions that reveal the presence of stellar companions.
“From detailed analysis of 150 of the most massive stars, we found that at least 70% are part of close binary systems,” Dr. Shenar noted. “This constitutes the first direct and convincing evidence that massive stars commonly existed in binaries even under the conditions of the early universe, perhaps even more frequently than today.”
The implications are far-reaching. Binary interactions affect how stars explode as supernovae, how black holes and neutron stars form, and how galaxies are enriched with the heavy elements essential for planets and life. “This finding fundamentally changes our view of how the first massive stars evolved and how they shaped the universe we see today,” Dr. Shenar said. “It shows that even in the earliest epochs, stars were not isolated—they interacted, merged, and left a lasting imprint on the cosmos.”
By revealing the prevalence of massive binaries in the early universe, the study helps scientists better understand the processes that ultimately led to the galaxies, stars, planets, and life we observe today.
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