Astronomers have long known that many of the largest stars in our Milky Way do not live alone but instead exist in pairs.
Now, an international team of 70 scientists has discovered that this is also true in galaxies far beyond our own, where the chemical environment is very different.
The finding suggests that massive stars across the universe—even those born billions of years ago—may have evolved alongside close companions.
The discovery was made using the European Southern Observatory’s Very Large Telescope in Chile, one of the most powerful telescopes on Earth. By studying the Small Magellanic Cloud, a nearby dwarf galaxy with very low levels of heavy elements, the researchers were able to look back in time.
“The Small Magellanic Cloud acts like a time machine,” explained Hugues Sana of KU Leuven in Belgium. “Its conditions resemble those of galaxies that existed when the universe was just a few billion years old.”
In the Milky Way, which is rich in metals such as iron, oxygen, and carbon, massive stars often have partners.
These so-called binary systems play a crucial role in how stars live and die. Interactions between the stars can affect their brightness, their lifespan, and even how they end as supernovae or black holes. Until now, however, astronomers did not know if the same was true in metal-poor galaxies like the Small Magellanic Cloud.
To find out, the researchers used a special instrument called FLAMES, which allows astronomers to observe more than a hundred stars at once.
Over three months, they focused on 139 massive O-type stars, each 15 to 60 times heavier than our sun. These stars are extremely hot, shine with dazzling brightness, and eventually explode in powerful supernova blasts, leaving behind black holes.
The team monitored the stars at nine different points in time, carefully measuring whether they were speeding up or slowing down. The results were striking: more than 70% of the stars showed signs of acceleration and deceleration, strong evidence that they were being tugged by a nearby partner star.
“This shows that even in the metal-poor environment of the Small Magellanic Cloud, massive stars often have companions,” said Julia Bodensteiner of the University of Amsterdam. “That means the first stars in the universe, which we also think were massive, may have formed in pairs as well. Some of these systems might have even become two black holes orbiting one another. It’s an exciting possibility.”
The researchers plan to continue their work, observing the same stars another 16 times. Their goal is to map out the orbits of these stellar pairs and learn more about their masses and the nature of their companions.
According to Tomer Shenar of Tel Aviv University, the results will provide valuable insights for scientists studying the young universe. “By understanding these massive binary stars better, we can give cosmologists and astrophysicists stronger tools to model the early, metal-poor cosmos.”
