A team of researchers from Tel Aviv University, in collaboration with KU Leuven and Amsterdam universities, has discovered that at least 70% of massive stars in the early universe were formed in binary systems – a finding that changes our understanding of the formation of black holes, supernovae, and the enrichment of galaxies in heavy elements.
A new study of School of Physics and Astronomy at Tel Aviv University reveals that most massive stars that formed in the early universe formed as binary systems, similar to the massive stars that form in our galaxy. The research team believes that these findings are the first strong evidence that massive binary stars were common – and perhaps even more common – in the early universe. Such systems have a wide range of effects, from the formation of black holes of all sizes, to the shaping of energetic supernovae, to the enrichment of galaxies in heavy elements.
The research was led by Dr. Tomer Shenhar from the School of Physics and Astronomy at Tel Aviv University and in collaboration with Dr. Hoog Sne from KU Leuven in Belgium and Dr. Julia Bodensteiner from the University of Amsterdam, Netherlands. The research was published in the journal Nature Astronomy.
The team of researchers explains that massive stars – those with a mass ten times or more than the Sun – are responsible for a host of cosmic phenomena. A single massive star can emit more energy than a million Sun-like stars. They shape the structure and properties of the galaxies they inhabit, create most of the heavy elements in the universe, and end their lives in powerful supernova explosions, leaving behind the most mysterious objects we know: neutron stars and black holes.
In our own galaxy, the Milky Way, most massive stars are known to be born in "binary systems" – pairs of stars in such close orbits that they exchange matter with each other and sometimes even merge during their lives. These interactions fundamentally change the course of the lives and deaths of massive stars.
Companions to the stars
A key question is whether this phenomenon of "pairing" among massive stars also characterized the massive stars that formed in the early universe. The James Webb Space Telescope is currently observing the first galaxies that formed after the Big Bang, and these galaxies indicate the presence of huge populations of massive stars, but the enormous distances to them prevent direct examination of the structure of the stellar systems there.
Dr. Shenhar says: "To circumvent this limitation, we developed an observational survey designed to study massive stars in a relatively nearby galaxy, but one that simulates the chemical conditions of the early universe. As part of the Binarity at LOw Metallicity (BLOeM) survey, we conducted a two-year observational campaign on the very large VLT telescope in Chile, during which spectra were taken of about 1,000 massive stars in the Small Magellanic Cloud – a nearby galaxy with a chemical composition low in metals, similar to the composition of the young universe."
"Spectral analysis of the data allows for the measurement of the periodic motion of the stars, and thus the inference of the existence of stellar companions," adds Dr. Shenhar. "From a detailed analysis of data for the 150 most massive stars, we found that at least 70% of them are part of close binary systems. This is the first direct and convincing evidence that massive stars were common in binary systems even under conditions that prevailed in the early universe, and perhaps even more common than today."
In summary, this finding changes our understanding of the processes that shaped the universe – from the formation of black holes of all sizes, through the characteristics of supernova explosions, to the enrichment of entire galaxies with the heavy elements necessary for the formation of stars, planets, and even life.
