Were massive stars in the early universe born in pairs?

A Scientific Breakthrough in Understanding the Formation of the Universe’s First Stars

Were massive stars in the early universe born in pairs?

A new study from the School of Physics and Astronomy at Tel Aviv University reveals that most massive stars formed in the early universe were born as binary systems, similar to the massive stars in our own galaxy. The research team estimates that these findings provide the first strong evidence that massive binary stars were commonin the early universe. Such systems influence the cosmos in many ways, from the creation of black holes of all sizes, through shaping energetic supernovae, to enriching galaxies with heavy elements.

The study was led by Dr. Tomer Shenar from the School of Physics and Astronomy at Tel Aviv University, Dr. Hugues Sana of KU Leuven University in Belgium, and Dr. Julia Bodensteiner of the University of Amsterdam, the Netherlands. The study was published in the journal Nature Astronomy.

The researchers explain that massive stars, those with at least ten times the mass of the Sun, are responsible for a variety of cosmic phenomena. A single massive star can emit more energy energy than a million Sun-like stars. Massive stars 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 the most mysterious objects we know: neutron stars and black holes.

In our galaxy, the Milky Way, it is well established that most massive stars are born in “binary systems”, pairs of stars in orbits so close that they exchange matter and sometimes even merge during their lifetimes. These interactions fundamentally alter the evolution and fate of the massive stars.

A key question is whether this phenomenon of “binarity” also characterized the massive stars that formed in the early universe. Today, the James Webb Space Telescope observes the first galaxies formed after the Big Bang, which indicate the presence of giant populations of massive stars, but their enormous distances prevent direct examination of their stellar system structures.

Dr. Shenar: “To overcome this limitation, we developed an observational survey designed to study massive stars in a relatively nearby galaxy that mimics the chemical conditions of 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 adds: “Spectral analysis of the data enables measurement of periodic motions of stars, thereby revealing 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. 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.”

In conclusion, this finding changes our understanding of the processes that shaped the universe, from the formation of black holes of all scales, through the nature of supernova explosions, to the enrichment of entire galaxies with the heavy elements necessary for the creation of stars, planets, and even life itself.

 

Link to the article:

https://www.nature.com/articles/s41550-025-02610-x

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