A new study from Tel Aviv University (TAU) has revealed that most massive stars in the early universe were likely born in pairs — orbiting closely together and interacting throughout their lives.
The discovery, published in Nature Astronomy, offers the strongest evidence yet that binary stars were common in the universe’s first generations of stars.
The study was led by Dr. Tomer Shenar from TAU’s School of Physics and Astronomy, along with Dr. Hugues Sana from KU Leuven University in Belgium and Dr. Julia Bodensteiner from the University of Amsterdam.
Their findings could reshape how scientists understand the evolution of galaxies, black holes, and even the origins of the elements that make life possible.
Massive stars are cosmic powerhouses — each one can be at least ten times heavier than the Sun and emit more energy than a million smaller stars like ours.
These stars play a crucial role in shaping galaxies, producing heavy elements, and ending their lives in enormous supernova explosions that leave behind neutron stars or black holes.
In the Milky Way, scientists already know that most massive stars form as binary systems, meaning two stars orbit so closely that they often share or exchange matter, sometimes even merging into one. These interactions drastically affect how such stars evolve and die.
The big question for astronomers has been whether this pairing behavior also existed in the early universe, just a few hundred million years after the Big Bang.
The James Webb Space Telescope (JWST) has shown that early galaxies contained many massive stars, but those galaxies are too distant for scientists to study individual stars in detail.
To overcome this challenge, Dr. Shenar and his team designed a creative workaround: they observed stars in a nearby galaxy that has a chemical makeup similar to that of the early universe.
This project, called Binarity at LOw Metallicity (BLOeM), focused on the Small Magellanic Cloud — a small galaxy near the Milky Way with very low metal content, much like the first galaxies.
Over two years, the researchers used the Very Large Telescope (VLT) in Chile to collect light spectra from about 1,000 massive stars in the Small Magellanic Cloud.
By carefully studying the patterns in the starlight, they were able to detect periodic changes that revealed whether the stars had close companions.
The results were striking: at least 70% of the 150 most massive stars studied were part of close binary systems.
This is the first strong evidence that even under early-universe conditions, massive stars frequently formed as pairs — and possibly even more often than they do today.
According to the researchers, these findings could change our understanding of how the universe evolved, influencing how black holes formed, how supernovae exploded, and how galaxies became enriched with the heavy elements that eventually made planets — and life — possible.
