Celestial monsters at the origin of globular clusters

May 12. (EUROPE PRESS) –

Astronomers believe they have discovered the first chemical trace attesting to the presence of massive stars in globular proto-clusters, born just 440 million years after the Big Bang.

globular clusters, the most massive and oldest in the universe of its kind, are very dense groups of stars distributed in a sphere, with a radius that varies from a dozen to a hundred light years. They can contain up to 1 million stars and are found in all kinds of galaxies. Ours is home to about 180 of them. One of its great mysteries is the composition of its stars: why is it so varied? For example, the ratio of oxygen, nitrogen, sodium, and aluminum varies from star to star. However, they were all born at the same time, within the same gas cloud. Astrophysicists speak of “abundance anomalies.”

A team from the Universities of Geneva (UNIGE) and Barcelona, ​​and the Institut d’Astrophysique de Paris (CNRS and Sorbonne University) have made a new breakthrough in explaining this phenomenon. In 2018 he had developed a theoretical model according to which supermassive stars would have “contaminated” the original gas cloud during the formation of these clusters, enriching their stars with chemical elements in a heterogeneous way.

“Today, thanks to data collected by the James Webb Space Telescope, we believe we have found a first clue to the presence of these extraordinary stars,” he explains. it’s a statement Corinne Charbonnel, full professor of the Department of Astronomy of the Faculty of Sciences of UNIGE, and first author of the study.

These celestial monsters are 5,000 to 10,000 times more massive and five times hotter at their center (75 million °C) than the sun. But proving its existence is complex. “Globular clusters are between 10 and 13 billion years old, while the maximum lifetime of superstars is two million years. Therefore, they disappeared very early from the clusters that can be observed today. Only indirect traces remain,” explains Mark Gieles, ICREA professor at the University of Barcelona and co-author of the study.

Thanks to the very powerful infrared vision of the James Webb telescope, the co-authors were able to support their hypothesis. The satellite captured the light emitted by one of the most distant and young galaxies known to date in our universe. Located about 13.3 billion light-years away, GN-z11 is only a few tens of million years old. In astronomy, the analysis of the light spectrum of cosmic objects is a key element to determine their characteristics. Here, the light emitted by this galaxy has provided two valuable pieces of information.

“It has been established that it contains very high proportions of nitrogen and a very high density of stars,” says Daniel Schaerer, Associate Professor at the Department of Astronomy at UNIGE’s Faculty of Sciences and co-author of the study.

This suggests that several globular clusters are forming in this galaxy and that they still harbor an active supermassive star. “The strong presence of nitrogen can only be explained by the combustion of hydrogen at extremely high temperatures.which only the core of supermassive stars can reach, as shown by the models of Laura Ramírez-Galeano, a master’s student in our team”, explains Corinne Charbonnel.

The researchers believe that these new results, which are published in the journal Astronomy & Astrophysics, strengthen their model, the only one currently capable of explaining abundance anomalies in globular clusters, they say. The next step for the scientists will be to test the validity of this model in other globular clusters that form in distant galaxies, using data from James Webb.