The Milky Way is not homogeneous as scientists thought

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The finding could force scientists to redefine theoretical model design to understand how the Milky Way and other galaxies evolved.

Astronomers have observed the composition of the gases in our galaxy and have shown that, contrary to the models established so far, they are not homogeneously mixed.

Until now, hypothetical models expected that three main elements that make up a significant part of our galaxy would mix homogeneously across the vast 105,700 light-year diameter of the Milky Way: gas from outside our galaxy, gas from inside our galaxy. galaxy –enriched with chemical elements– and the dust created by the condensation of the metals present in this gas. 

But a new study by a team of astronomers from the University of Geneva (UNIGE) shows that these gases are not homogeneously mixed and reached a level of chemical enrichment similar to that of the Sun’s atmosphere, called solar metallicity, according to the statement. UNIGE press release. The team’s research was published in the journal Nature.

Calculate the composition of gas and dust in the atmosphere of stars

With the help of the Hubble Space Telescope and the Very Large Telescope, located in the Atacama desert region of northern Chile, astronomers from the University of Geneva (UNIGE) used a new technique to calculate the total composition of the gas and dust in the atmosphere of stars throughout the Milky Way.

This allowed them to track the total amount of metals in the powder and compare it to the totals previously obtained. What they found is that the stars in some areas had only 10 percent of the heavy elements that our star, the Sun, has.

Gases, metals and elements in the formation and death of stars

“The galaxies feed on the ‘virgin’ gas that falls from the outside, which rejuvenates them and allows the formation of new stars,” says Annalisa De Cia, professor in the Department of Astronomy of the Faculty of Sciences of the UNIGE and first author of the study. 

According to the statement, the stars, at the same time, burn the hydrogen that constitutes them throughout their lives and form other elements through nucleosynthesis. 

When stars reach the end of their life, they explode into powerful and violent supernovae. This scatters the metals it has produced, such as iron, zinc, carbon and silicon, introducing these elements into the gas of the galaxy, which clump together in cold regions.

“Initially, when the Milky Way was formed, more than 10,000 million years ago, it had no metals. Later, the stars were enriching the environment with the metals they produced,” says Annalisa De Cia.

Radically different or unique compositions

Thus, the consensus so far was that the amount of metals found in the Sun’s atmosphere, known as solar metallicity, was common to stars, gas clouds, and other bodies throughout the Milky Way. Therefore, such solar metallicity could be used as a measure of chemical abundance in our galaxy.

However, the new research suggests that this might not be the case after all. Stars and planets could form from gases with radically different or unique compositions.

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

“From now on, we will have to refine the simulations by increasing the resolution, to be able to include these metallicity changes in different places in the Milky Way.”