An international team led by scientists from Belgium, the Netherlands and Tel Aviv University has found that over 70% of the massive stars in the Small Magellanic Cloud have partners – a finding that sheds new light on the first stars in the universe and the way they evolved into black holes.
Massive stars in metal-poor galaxies tend to have close companions, similar to massive stars in the metal-rich Milky Way galaxy, an international team of 70 astronomers from Belgium, the Netherlands and Israel has discovered. The researchers used the European Southern Observatory's Very Large Telescope (VLT) in Chile to track the velocities of massive stars in the Small Magellanic Cloud.
The study was published in the journal Nature Astronomy.
For twenty years, astronomers have known that many of the massive stars in the Milky Way have partners. In recent years, it has become clear that the interaction between the partners is critical to their evolution. However, it was unclear whether a similar pattern existed for massive stars in metal-poor galaxies—and now it turns out that it does.
Cosmic time machine
"We used the Small Magellanic Cloud as a time machine," explained Hoge Sanne of the University of Leuven (Belgium). "The metallicity conditions there represent the environment of distant galaxies when the universe was only a few billion years old."
Studying stars outside the Milky Way is difficult because the stars are very far away and their light is weak. The researchers used a spectrograph FLAMES On the VLT telescope – one of the largest in the world – which allows 132 different stars to be measured simultaneously.
Accelerators and decelerators
Over a three-month period, 139 massive O-type stars, with masses ranging from 15 to 60 solar masses, were observed at nine different times. These stars are hot, bright, and end their lives in supernovae in which the star's core collapses into a black hole.
The results showed that over 70% of the stars examined were accelerating and decelerating – a clear sign that they had close companions.
"The fact that massive stars in the Small Magellanic Cloud have partners suggests that the first stars in the universe – which were probably very massive – also had partners," said Julia Bodensteiner of the University of Amsterdam. "Some of these systems may have ended up as two black holes orbiting each other. It's a fascinating thought."
Looking ahead
In the next phase, the researchers plan 16 additional observations of the same stars in order to reconstruct the orbits of the pairs, determine their masses, and study the nature of the pairs.
"Our measurement technologies will provide astrophysicists studying the young, metal-poor universe with a solid foundation for understanding binary systems of massive stars," concluded Dr. Tomer Shaner of Tel Aviv University.
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