2023-05-31 13:15:20
The chemical composition of stars born in the oldest and most massive star clusters in the universe shows anomalies not found in any other population of stars.
A team from the universities of Geneva, Paris and Barcelona, with the participation of the Institute for Space Studies of Catalonia (IEEC) through the Institute of Cosmos Sciences (ICC) of the University of Barcelona (UB), has found traces of stars supermassive that can explain the anomalies observed in large star clusters.
Globular clusters are very dense groups of stars distributed in a sphere, with a radius that varies between ten and a hundred light-years. They can contain up to a million stars and are found in all kinds of galaxies. Ours houses about 180 of them. One of the great mysteries is the composition of its stars: why is it so varied? As an 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 call these “abundance anomalies.”
The research team, made up of specialists from the University of Geneva (UNIGE), the IEEC, the Institute of Cosmic Sciences, and the Paris Institute of Astrophysics (affiliated to the CNRS (French National Center for Scientific Research) and the University of the Sorbonne) has made a new advance in the explanation of this phenomenon.
In 2018, the team 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 heterogeneous ways. “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,” explains Corinne Charbonnel, Senior Lecturer in the Department of Astronomy at UNIGE’s Faculty of Sciences and co-author. of the study.
These celestial monsters were between 5,000 and 10,000 times more massive and five times hotter at their center (75 million degrees Celsius) than the Sun. But proving their 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 currently observable clusters. Only indirect traces remain”, explains Mark Gieles, ICREA professor and IEEC researcher at the Institute of Cosmos Sciences (ICC) of the University of Barcelona, co-author of the study.
A typical globular cluster, Messier 13 (M13). (Photo: NASA / ESA / Hubble Heritage Team (STScI / AURA). With the collaboration of: C. Bailyn (Yale University), W. Lewin (Massachusetts Institute of Technology), A. Sarajedini (University of Florida), and W van Altena (Yale University))
Thanks to the extremely powerful infrared vision of the James Webb Space Telescope, the study authors have managed to corroborate their hypothesis. The space observatory captured the light emitted by a galaxy located some 13.3 billion light-years away. It is one of the most distant known. And, considering that we see it as it was 13.3 billion years ago, in the infancy of the universe, it is also, observationally, one of the most primitive known.
This galaxy, called GN-z11, is only a few tens of millions of years old as we now see it from this point in the universe.
In astronomy, the analysis of the light spectrum of cosmic objects is a key resource to determine their characteristics. In this case, the light emitted by the 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.
This suggests that several globular clusters are (were) forming in this galaxy and that it still hosts an active supermassive star, since the strong presence of nitrogen can only be explained by the nuclear combustion of hydrogen at extremely high temperatures, which only the core of supermassive stars can reach.
These new results reinforce the international team’s model, the only one currently capable of explaining the aforementioned anomalies in globular clusters.
The scientists’ next step will be to test the validity of this model in other globular clusters that form in distant galaxies, using data from the James Webb Space Telescope.
The study is titled “N-enhancement in GN-z11: First evidence for supermassive stars nucleosynthesis in proto-globular clusters-like conditions at high redshift?” And it has been published in the academic journal Astronomy and Astrophysics. (Source: IEEC / ICCUB / Université de Genève)
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