✨ Our galaxy has a typical chemical signature, the explanation found

The stars in our galaxy exhibit a curious chemical division, but is this the norm in the Universe? A recent study shows that this peculiarity is not a general rule, opening the door to a great diversity in galactic evolution.

Researchers used advanced computer simulations to model galaxies similar to the Milky Way. These models, developed as part of the Auriga project, allow for the reconstruction of the formation and evolution of these structures over billions of years. Furthermore, by analyzing thirty virtual galaxies, the team was able to identify several mechanisms behind the observed chemical signatures.


In the Milky Way, astronomers distinguish two groups of stars based on their proportions of iron and magnesium. This separation, called chemical bimodality, has long been considered an open question. It appears clearly in diagrams, even though stars sometimes share similar levels of heavy elements. This feature is not unique, but its presence differs from one galaxy to another.

The simulations reveal that this chemical duality can emerge through different pathways. For example, some galaxies develop it thanks to intense episodes of star formation, alternating with calmer phases. Others see this pattern form due to changes in incoming gas flows. Contrary to a widespread idea, a past collision with a dwarf galaxy is not necessary to explain this phenomenon.

The study highlights the role of metal-poor gas from the galactic environment. This material contributes to the creation of the second group of stars, gradually enriching the galaxy. Consequently, the precise shape of each chemical sequence is closely linked to the history of star formation, which explains why each galaxy can have a unique profile.

New telescopes, like the James Webb Space Telescope, will allow testing these predictions by observing distant galaxies. These instruments will provide more precise measurements of stars, helping to refine models of galactic evolution. Thus, researchers anticipate a great diversity in chemical sequences across the Universe, which will improve our understanding of the Milky Way and its counterparts.

This simulation-based approach thus shows that the Milky Way is not an archetype, but an example among others. The diversity of evolutionary trajectories highlights the numerous cosmic processes, where each galaxy follows its own path to shape its stellar population.

Chemical bimodality in stars

Chemical bimodality refers to the presence of two distinct groups of stars within a galaxy, characterized by different ratios of elements like iron and magnesium. This division is detected by analyzing starlight, which reveals their chemical composition. It offers a window into the conditions of star formation and a galaxy's history of metal enrichment.

This feature is particularly visible in the Milky Way, where stars near the Sun clearly show these two sequences. It results from processes such as supernovae, which disperse heavy elements into the interstellar medium. Over time, these events modify the chemistry of the gas from which new stars form, creating stellar generations with distinct signatures.

Understanding this bimodality helps astronomers trace galactic evolution. By studying how element proportions change, they can deduce star formation rates, past mergers, and gas flows. This allows building a detailed timeline of a galaxy's life, from its beginnings to its current state.

This notion is fundamental for interpreting observations from modern telescopes. It guides theoretical models and simulations by providing constraints on the mechanisms that shape galaxies. In this way, stellar chemistry becomes a powerful tool for exploring the Universe on a large scale.