June 19, 2024

Astronomers Discover the Least “Metallic” Stellar Structure in the Milky Way

Observations using the Gemini North telescope– part of the worldwide Gemini Observatory, a Program of NSFs NOIRLab– reveal that the stars in this stream were when part of an ancient globular star cluster that was torn apart by gravitational interactions with our galaxy. The abundance of these heavier elements in a star is called its metallicity, and differs from star to star. Not just does this discovery challenge our current understanding and designs of the formation of these stellar groupings, which exclude the existence of structures made up only of such stars, it also opens a special and direct window onto the extremely earliest ages of star development and the development of stellar structures in the extremely far-off past. Since heavy elements were produced by successive generations of massive stars, the really low metallicity of the C-19 stars shows that they were formed only a brief time after the birth of the Universe.

For more on this discovery, see Ruins of Ancient Star Cluster Discovered at the Fringes of Our Galaxy.
Recommendation: “A stellar stream residue of a globular cluster below the metallicity floor” by Nicolas F. Martin, Kim A. Venn, David S. Aguado, Else Starkenburg, Jonay I. González Hernández, Rodrigo A. Ibata, Piercarlo Bonifacio, Elisabetta Caffau, Federico Sestito, Anke Arentsen, Carlos Allende Prieto, Raymond G. Carlberg, Sébastien Fabbro, Morgan Fouesneau, Vanessa Hill, Pascale Jablonka, Georges Kordopatis, Carmela Lardo, Khyati Malhan, Lyudmila I. Mashonkina, Alan W. McConnachie, Julio F. Navarro, Rubén Sánchez-Janssen, Guillaume F. Thomas, Zhen Yuan and Alessio Mucciarelli, 5 January 2022, Nature.DOI: 10.1038/ s41586-021-04162-2.
This work was brought out as part of the Pristine survey, with ESAs Gaia area observatory, the Canada-France-Hawaii Telescope (Hawaii), the Gemini North telescope (Hawaii) and the GTC telescope (Canary Islands).

This illustration reveals the place of the C-19 outstanding stream (orange, vertical stream of stars in lower left), which was recently discovered at the edge of our Milky Way Galaxy. Observations utilizing the Gemini North telescope– part of the worldwide Gemini Observatory, a Program of NSFs NOIRLab– reveal that the stars in this stream were once part of an ancient globular star cluster that was torn apart by gravitational interactions with our galaxy.
98.5% of the Sun is made up of 2 light chemical elements, hydrogen and helium, while the staying 1.5% includes other heavier components such as iron, oxygen, and carbon. The abundance of these heavier elements in a star is called its metallicity, and varies from star to star. It now turns out that our Galaxy is home to an outstanding structure distinctively made of stars with extremely low metallicity, with a heavy component content 2,500 times lower than that of the Sun. This is well below that of any other recognized outstanding structure in deep space.
This discovery, made by a global group led by a CNRS scientist at the Strasbourg Astronomical Observatory (CNRS/ University of Strasbourg), and including researchers from the Galaxies, Stars, Physics and Instrumentation Laboratory (Paris Observatory– PSL/ CNRS) and at the J-L Lagrange Laboratory (CNRS/ Côte dAzur Observatory), is published on January 5, 2022, in the journal Nature.
Credit: Distribution of extremely dense groups of stars in the Milky Way, called globular clusters, superimposed on a map of the Milky Way compiled from information gotten with the Gaia Space Observatory. Each dot represents a cluster of a couple of thousand to a number of million stars, as in the insert image of the Messier 10 cluster.
This group of stars all come from an excellent structure in the Milky Way called C-19. Not just does this discovery obstacle our existing understanding and designs of the formation of these excellent groupings, which exclude the presence of structures composed just of such stars, it also opens a unique and direct window onto the extremely earliest ages of star development and the development of outstanding structures in the really far-off past. Since heavy elements were produced by succeeding generations of massive stars, the extremely low metallicity of the C-19 stars shows that they were formed just a short time after the birth of deep space.