Globular clusters like M13 in the image above are swarms of up to a million ancient stars tightly packed in volumes just a hundred light years or so across. They are thought to have formed 10 to 13 billion years ago, when the universe was in its infancy, and are found in all types of galaxies. The Milky Way hosts about 180 such clusters.
One of the many questions about globular clusters concerns the abundances of the elements seen in the spectra of their suns. The stars all formed at roughly the same time, from the same cloud of raw materials, but the proportions of elements like oxygen, nitrogen, sodium and aluminium can vary from star to star.
Researchers at the universities of Genéve (UNIGE), Barcelona and the Institut d’Astrophysique de Paris (CNRS and Sorbonne University) developed a theoretical model in 2018 in which supermassive stars five times hotter and 5,000 to 10,000 times “heavier” than the Sun could have played a role by “polluting” the original gas cloud with elements cooked up in their cores.
Using the James Webb Space Telescope, the team studied light emitted from one of the most distant and youngest galaxies yet found some 13.3 billion light years away.
The spectra “contains very high proportions of nitrogen and a very high density of stars,” said Daniel Schaerer, associate professor in the Department of Astronomy at the UNIGE Faculty of Science, and co-author of the study.
The data suggest several globular clusters are forming in the galaxy and that they still harbour active supermassive stars.
“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,” said team member Corinne Charbonnel.
While the Webb data support the theoretical model, more observations of additional globular clusters are needed to confirm its validity.