Monstrous superstars would have dominated the cosmic dawn

Monster superstars would have dominated the cosmic dawn CREDITS: HST-STSCL-NASA-ESA.

Scientists have found compelling evidence for the existence of supermassive stars inside globular clusters, when they formed 13 billion years ago.

Gigantic stars with masses reaching 10,000 suns would have been common in the early Universe, according to a new study. New observations with NASA’s James Webb Space Telescope have identified some traces of these huge superstars in the distant galaxy GN-z11, seen as it looked just 440 million years after the Big Bang.

An international team of researchers from the University of Geneva (UNIGE), in Switzerland, the University of Barcelona, ​​in Spain, and the Institute of Astrophysics in Paris, in France, has discovered the first chemical trace attesting to the presence of supermassive stars. 5,000 to 10,000 times more massive than the Sun, during the formation of globular clusters at the beginning of the cosmos.

Astronomers define globular clusters as extremely dense collections of stars, distributed in a sphere with a radius ranging from a dozen to a hundred light-years. In that contained space, they can accumulate up to a million stars and are found in all types of galaxies. In the Milky Way, for example, there are about 180 globular clusters.

One of the great mysteries surrounding these fantastic cosmic structures is the composition of their stars, which is characterized by its great variety. This can be seen in the distribution of the elements, with a proportion of oxygen, nitrogen, sodium or aluminum that varies remarkably from one star to another. Taking into account that all the stars that are part of a globular cluster were born at the same time and within the same gas cloud, scientists are trying to determine why they register so many differences, since supposedly they should be more homogeneous. To discover these apparent anomalies, they try to observe the most distant structures, in a “snapshot” of the Universe as it looked shortly after the Big Bang.

Taking advantage of NASA’s James Webb Space Telescope (JWST) for such purposes, the researchers tried to test the presence of superstars in these globular clusters during their formation. The task is not easy: while globular clusters are between 10 and 13 billion years old, the maximum lifetime of superstars is two million years.

In this way, since they vanished very quickly from the clusters that can currently be observed, it is only possible to verify the existence of these supermassive stars through indirect chemical traces. Doing so is crucial to solving some of the mysteries behind globular clusters and thus furthering our understanding of the Cosmic Dawn, which began approximately 250 million years after the initial outburst, or Big Bang, and marked the formation of the first stars. and galaxies. According to a press release, JWST captured the light emitted by one of the most distant galaxies known to date, located some 13.3 billion light-years away from Earth. It is called GN-z11 and is only a few tens of million years old, indicating that it was captured in its youth, approximately 440 million years after the Big Bang.

The analysis of the light spectrum of this galaxy yielded important information: as explained by the scientists in the new study, recently published in the journal Astronomy & Astrophysics, the very high proportions of nitrogen and an extremely high density of stars suggest that they are forming several globular clusters in this galaxy, and which 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,” concluded Corinne Charbonnel, lead author of the research. For scientists, these data are proof that these monstrous stars were present within the clusters when they formed, at a time when the Universe was just over 400 million years old.

Reference N-enhancement in GN-z11: First evidence for supermassive stars nucleosynthesis in proto-globular clusters-like conditions at high redshift? C. Charbonnel et al. Astronomy & Astrophysics (2023). DOI: