Star clusters orbiting the outskirts of the Milky Way shed new light on the evolution of our galaxy as well as the elusive dark matter that surrounds it.
Scientists at the Carnegie Institution for Science have mapped a dozen associations of stars that orbit in the halo of gas that envelops our galaxy, the Milky Way. The stars form elongated threads, called stellar fluxes, that surround the edges of the host galaxy. Studying these stellar structures helps astronomers better understand the distribution of black matter in our galaxy and retrace how the galaxy developed over time as it devoured smaller clusters of stars.
Dark matter is the invisible substance that makes up up to 85% of all matter in the universe. It has never been seen but must exist to make sense of the gravitational forces observed in the galaxy, which keep stars in their orbits
“Star streams are the jagged remains of little neighbors galaxies and star clusters torn apart by the Milky Way, ”said Josh Simon, study co-author and Carnegie Institution for Science astronomer, in a report. declaration. “These remains continue to move together in long, arching threads, orbiting our galaxy.”
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Previous studies have focused on individual streams, but the purpose of this study was to measure the properties of as many stellar streams as possible.
“When studied in groups, the properties of these stellar streams reveal the presence of the invisible dark matter of the Milky Way in the same way that twinkling lights can reveal the shape of a tree around which they hang, even when we may not see the branches or the foliage, ”the scientists said in the release.
Use of the Anglo-Australian telescope, located at the Siding Spring observatory in Australia, as well as data from the European Space Agency (ESA) Gaia Space Telescope, the researchers measured the speeds at which streams orbit the Milky Way and analyzed their chemical composition.
The fact that stars in these streams have a distinct chemical composition compared to most stars in the Milky Way provides evidence that they did indeed arrive from different stellar populations, dwarf galaxies and star clusters that were captured by the gravitational pull of the largest galaxy hundreds of millions and billions of years ago.
“We find that these flows are disrupted by the gravitational pull of the Milky Way and eventually become part of the Milky Way,” Ting Li, lead author of the University of Toronto study, said in the release. . “This study gives us an overview of the Milky Way eating habits, such as the types of smaller star systems it “eats”. As our galaxy ages, it gets bigger. “
Understanding how the Milky Way gradually devours the small galaxies that fall between its clutches helps astronomers unravel the evolution of the galaxy over billions of years since the first stars that came together after the big Bang to the massive galaxy of hundreds of billions of stars we see today.
The study, which is part of the Southern Stellar Stream Spectroscopic Survey (S5), has been accepted for publication in The Astrophysical Journal.
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