In order to better understand the history and evolution of the Milky Way, astronomers are studying the composition of the gases and metals that make up an important part of our galaxy. Three main elements stand out: the initial gas coming from outside our galaxy, the gas between the stars inside our galaxy — enriched with chemical elements –, and the dust created by the condensation of the metals present in this gas. Until now, theoretical models assumed that these three elements were homogeneously mixed throughout the Milky Way and reached a level of chemical enrichment similar to the Sun’s atmosphere, called the Solar metallicity. Today, a team of astronomers demonstrates that these gases are not mixed as much as previously thought, which has a strong impact on the current understanding of the evolution of galaxies. As a result, simulations of the Milky Way’s evolution will have to be modified.