Clouds and streams of cosmic beautiful gas (magenta) accrete onto the Milky Way, however this gas does not effectively blend in the Galactic disk, as highlighted for the Solar community (zoom-in). Credit: © Dr Mark A. Garlick
Astronomers from the UNIGE have actually observed the structure of the gases in our galaxy and have actually revealed that, contrary to the designs developed previously, they are not homogeneously blended.
In order to much better comprehend the history and advancement of the Milky Way, astronomers are studying the structure of the gases and metals that comprise a fundamental part of our galaxy. Three primary components stick out: the preliminary gas originating from outside our galaxy, the gas in between the stars inside our galaxy– enriched with chemical components– and the dust developed by the condensation of the metals present in this gas. Until now, theoretical designs presumed that these 3 components were homogeneously blended throughout the Milky Way and reached a level of chemical enrichment comparable to the Sun’s environment, called the Solar metallicity.
Today, a group of astronomers from the University of Geneva (UNIGE) shows that these gases are not blended as much as formerly believed, which has a strong effect on the present understanding of the advancement of galaxies. As an outcome, simulations of the Milky Way’s advancement will need to be customized. These results can be checked out in the journal Nature
Galaxies are comprised of a collection of stars and are formed by the condensation of the gas of the intergalactic medium made up of primarily hydrogen and a little bit of helium. This gas does not consist of metals unlike the gas in galaxies– in astronomy, all chemical components much heavier than helium are jointly called “metals,” although they are atoms in gaseous kind.
“Galaxies are fuelled by ‘virgin’ gas that falls in from the outside, which rejuvenates them and allows new stars to form,” discusses Annalisa De Cia, a teacher in the Department of Astronomy at the UNIGE Faculty of Science and very first author of the research study. At the very same time, stars burn the hydrogen that constitutes them throughout their life and form other components through nucleosynthesis.
When a star that has actually reached completion of its life takes off, it expels the metals it has actually produced, such as iron, zinc, carbon and silicon, feeding these components into the gas of the galaxy. These atoms can then condense into dust, particularly in the cooler, denser parts of the galaxy.
“Initially, when the Milky Way was formed, more than 10 billion years ago, it had no metals. Then the stars gradually enriched the environment with the metals they produced,” continues the scientist. When the quantity of metals in this gas reaches the level that exists in the Sun, astronomers mention Solar metallicity.
A not so uniform environment
The environment that comprises the Milky Way therefore unites the metals produced by the stars, the dust particles that have actually formed from these metals, however likewise gases from outside the galaxy that routinely enter it.
“Until now, theoretical models considered that these three elements were homogeneously mixed and reached the Solar composition everywhere in our galaxy, with a slight increase in metallicity in the center, where the stars are more numerous,” discusses Patrick Petitjean, a scientist at the Institut d’Astrophysique de Paris, SorbonneUniversity “We wished to observe this in information utilizing an Ultraviolet spectrograph on the Hubble Space Telescope“
Spectroscopy permits the light from stars to be separated in its private colors or frequencies, a bit like a with prism or in a rainbow. In this decayed light, astronomers are especially thinking about absorption lines: “When we observe a star, the metals that make up the gas between the star and ourselves absorb a very small part of the light in a characteristic way, at a specific frequency, which allows us not only to identify their presence, but also to say which metal it is, and how abundant it is,” he continues.
A brand-new approach established to observe the overall metallicity
For 25 hours, the group of researchers observed the environment of 25 stars utilizing Hubble and the Very Large Telescope (VLT) inChile The issue? The dust can not be counted with these spectrographs, although it includes metals. Annalisa De Cia’s group has actually for that reason established a brand-new observational method. “It involves taking into account the total composition of the gas and dust by simultaneously observing several elements such as iron, zinc, titanium, silicon, and oxygen,” discusses the Geneva scientist. “Then we can trace the quantity of metals present in the dust and add it to that already quantified by the previous observations to get the total.”
Thanks to this double observation method, the astronomers have actually discovered that not just is the Milky Way’s environment not uniform, however that a few of the locations studied reach just 10% of the Solar metallicity. “This discovery plays a key role in the design of theoretical models on the formation and evolution of galaxies,” states Jens-Kristian Krogager, scientist at the UNIGE’s Department ofAstronomy “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 locations in the Milky Way.”
These outcomes have a strong effect on our understanding of the advancement of galaxies and of our own in specific. Indeed, metals play a basic function in the development of stars, cosmic dust, particles, and worlds. And we now understand that brand-new stars and worlds might be formed today from gases with extremely various structures.
Reference: “Large Metallicity Variations in the Galactic Interstellar Medium” 8 September 2021, Nature
DOI: 10.1038/ s41586-021-03780 -0
