Découverte des étoiles les moins "métalliques" de la Voie lactée - Observatoire de Paris - PSL - Centre de recherche en astronomie et astrophysique

The Sun is composed of 98.5% of two light atomic elements, hydrogen and helium, and 1.5% of other heavier elements such as carbon, oxygen, iron ... This share of heavy atoms called "metallicity" of the star varies from one star to another. An international team led by a CNRS researcher at the Strasbourg Astronomical Observatory (CNRS/University of Strasbourg), involving researchers from the Laboratoire Galaxies, étoiles, physique, instrumentation (Observatoire de Paris - PSL/CNRS) and from the Laboratoire J-L Lagrange (CNRS/Observatoire de la Côte d’Azur), has just demonstrated that our galaxy harbors a group of stars with extremely low metallicity: These stars have heavy element contents 2500 times lower than those found in the Sun, well below those of any other known star in the Universe. These stars all belong to a stellar structure called C-19.

In addition to challenging current knowledge and models that do not consider that such stars exist, this discovery opens a direct and unique window on the early ages of star formation and on the establishment of stellar structures at this very early time. As heavy elements are produced by successive generations of massive stars, the very low "metallicity" of C-19 stars indicates that they formed in the early ages of the universe. The results of this research [1] are published on January 6, 2022 in the journal Nature.

Distribution des groupes très denses d'étoiles, appelées amas globulaires, de la Voie Lactée superposée sur la carte de la Voie Lactée construite à partir des données de la sonde Gaia. Chaque point est un regroupement de quelques milliers à plusieurs millions d'étoiles, comme sur l'image en insert de l'amas Messier 10. La couleur des points représente leur métallicité, c'est-à-dire leur quantité d'éléments lourds par rapport au Soleil. Les étoiles de C-19 sont indiquées par les symboles bleu clair. — Distribution of very dense groups of stars, called globular clusters, in the Milky Way superimposed on the map of the Milky Way built from Gaia data. Each point is a grouping of a few thousand to several million stars, as in the insert image of the Messier 10 cluster. The color of the dots represents their metallicity, i.e. their amount of heavy elements relative to the Sun. The C-19 stars are indicated by the light blue symbols.

© N. Martin/Observatoire astronomique de Strasbourg/CNRS ; Canada-France-Hawaii Telescope / Coelum; ESA/Gaia/DPAC

Bibliography

A stellar stream remnant of a globular cluster below the metallicity floor. Nicolas F. Martin et al. Nature, January 6, 2022.

[1] This work was carried out within the framework of the Pristine project, with the ESA’s Gaia probe, the Canada-France-Hawaii Telescope (Hawaii), the Gemini North Telescope (Hawaii) and the Large Telescope of the Canary Islands

Last update on 11 February 2022

Discovery of the less "metallic" stars of the Milky Way

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