The Milky Way galaxy is not homogeneous as previously thought: astronomers

London: Astronomers have observed the composition of the gases in our galaxy and have shown that, unlike the models established so far, they are not mixed evenly.

To understand the history and evolution of the Milky Way, astronomers have studied the composition of gases and metals that make up an important part of our galaxy. Three main elements stood out: the initial gas coming from outside our galaxy, the gas between the stars inside our galaxy – enriched in chemical elements -, and the dust created by the condensation of the metals present in this gas.

“Until now, the theoretical models considered that these three elements were mixed in a homogeneous way and reached the solar composition everywhere in our galaxy, with a slight increase in the metallicity in the center, where the stars are more numerous”, adds Patrick Petitjean. , researcher at the Institut d’Astrophysique de Paris, Sorbonne University in Paris, France.

For 25 hours, a team of scientists observed the atmosphere of 25 stars using Hubble and the Very Large Telescope (VLT) in Chile. They discovered that dust cannot be counted with these spectrographs, even though it contains metals.

A team from the University of Geneva (UNIGE) in Geneva, Switzerland, therefore developed a new observation technique and demonstrated that these gases do not mix as much as previously thought.

“This involves taking into account the total composition of gas and dust by simultaneously observing several elements such as iron, zinc, titanium, silicon and oxygen. Then, we can trace the quantity of metals present in the dust and add it to that already quantified by previous observations to obtain the total ”, declared Annalisa De Cia, professor in the Department of Astronomy at UNIGE.

The environment that makes up the Milky Way gathers the metals produced by the stars, the dust particles that are formed from these metals, but also gases outside the galaxy that enter it regularly, they explained.

Following the results, detailed in the journal Nature, the simulations of the evolution of the Milky Way will have to be modified.

“This discovery plays a key role in the design of theoretical models on the formation and evolution of galaxies,” said Jens-Kristian Krogager, researcher at the Department of Astronomy at UNIGE.

“From now on, we will have to refine the simulations by increasing the resolution, so that we can include these changes in metallicity at different places in the Milky Way,” Krogager added.