New insights about the chemical history of the Milky Way
A team from the Institute of Cosmos Sciences at the University of Barcelona (ICCUB) has published a paper that reveals previously unknown details about how galaxies such as the Milky Way form and evolve, and why their stars show surprising chemical patterns.
A team from the Institute of Cosmos Sciences at the University of Barcelona (ICCUB) has published a paper that reveals previously unknown details about how galaxies such as the Milky Way form and evolve, and why their stars show surprising chemical patterns.
A study published in Monthly Notices of the Royal Astronomical Society analyses the origin of an intriguing phenomenon known as chemical bimodality: the existence of two populations of stars with different chemical compositions. The study reveals that galaxies such as the Milky Way can develop two distinct chemical sequences through various processes.
The study is led by teams from the Institute of Cosmos Sciences at the University of Barcelona (ICCUB), the Institute of Space Studies of Catalonia (IEEC) and the National Centre for Scientific Research (CNRS, France), in collaboration with scientists from Liverpool John Moores University (United Kingdom) and the Max Planck Institute for Astrophysics (Germany).
What is chemical bimodality?
In some cases, this bimodality arises from bursts of star formation followed by periods of calm, while in others it is caused by changes in the inflow of gas from the galactic environment. Contrary to what had been thought, collision with a smaller galaxy known as Gaia-Sausage-Enceladus (GSE) is not required for the emergence of this chemical pattern. Simulations indicate that the metal-poor gas in the circumgalactic medium (CGM) plays a fundamental role in the formation of the second sequence of stars. Furthermore, the shape of these chemical sequences is closely linked to the star formation history of the galaxy.
With data provided by telescopes such as the James Webb Space Telescope (JWST) and missions such as PLATO and Chronos, researchers will be able to test these conclusions and refine our understanding of the universe.
“These results predict that other galaxies should also show a wide variety of chemical sequences. We will soon be able to verify this with the arrival of 30-metre telescopes, which will routinely perform these analyses on external galaxies. In the long run, these studies will allow us to further refine the physical evolutionary path of our own Milky Way,” says Chervin Laporte (ICCUB-IEEC, Paris Observatory and Kavli IPMU)
Multimedia gallery
Computer simulation of Milky Way-like galaxy in the Auriga suite
Computer simulation of a galaxy similar to the Milky Way from the Auriga suite, alternating between views of the stars, gas colored by iron (Fe) abundance, and gas colored by magnesium (Mg) abundance. The galaxy has developed a large, flat gas disc that forms a thin disc of young, blue stars. The gas disc was thicker in earlier stages, which produces an older, redder stellar population in a thicker stellar disc. A scale bar in the lower-left corner indicates the size of the galaxy. For comparison, the Sun is located about eight kiloparsecs (kpc) from the center of the Milky Way. Source: Matthew D. A. Orkney (ICCUB-IEEC)/Auriga project.
References
Orkney, Matthew et al. «The Milky Way in context: The formation of galactic discs and chemical sequences from a cosmological perspective». Monthly Notices of the Royal Astronomical Society, December 2025. DOI:10.1093/mnras/staf1551.