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The Milky Way’s Feeding Habits Shine a Light on Dark Matter

An artist’s expression of the Milky Way galaxy surrounded by dozens of star streams. These streams were satellite galaxies or globular clusters that are currently being torn by the gravity of our galaxies.Credits: James Josephides and S5 collaboration

Astronomers are one step closer to characterizing the dark matter that surrounds us. Milky Way The galaxy thanks to a new map of the flow of 12 stars orbiting the galactic halo.

Understanding the flow of these stars is very important for astronomers. It not only reveals the dark matter that puts the stars in orbit, but also tells us about the history of the formation of the Milky Way. The Milky Way has grown steadily for billions of years by shredding and consuming small star systems.


A movie showing the 3D positions of individual stars in a dozen streams observed by S5. The color of the individual dots depends on the 3D speed of the star.Credits: Sergey Koposov, S5 Collaboration

“We see these streams being disturbed by the Milky Way’s gravitational pull and eventually becoming part of the Milky Way. This study shows that the Milky Way’s” eat “types of small star systems, etc. Provides a snapshot of your eating habits. Our galaxies are getting thicker as we get older, “said Professor Ting Li of the University of Toronto, the lead author of this paper.

Professor Lee and her international collaborative research team have launched a dedicated program – South Star Stream Spectroscopy (S5) – to measure the characteristics of stellar streams. Milky Way.

Twelve stellar streams observed by S5

Impressions of the artist of the 12 stellar streams observed by S5, as seen from the South Pole of the galaxy.Credits: Geraint F. Lewis, S5 collaboration

Li and her team were the first to study such a rich collection of stellar flows by measuring star velocity using the Anglo-Australian Telescope (AAT), Australia’s 4-meter optical telescope. Group of people. Li and her team used Doppler light shifts, the same characteristics radar guns use to catch speed-violating drivers, to find out how fast individual stars are moving.

Unlike previous studies that focused on one stream at a time, “S5 is dedicated to measuring as many streams as possible and is very efficient using AAT’s unique capabilities. It can be measured, “commented Professor Daniel Zucker of Macquarie University. ..

A dozen streams that Gaia saw across the sky

The position of the stars in a dozen streams seen across the sky. In the background, the stars of the Milky Way from the European Space Agency’s Gaia project are shown. Since AAT is a telescope in the Southern Hemisphere, only the stream in the southern sky is observed in S5.Credits: Ting Li, S5 Collaboration and European Space Agency

The characteristics of the stellar stream reveal the presence of invisible dark matter in the Milky Way. “Think of the Christmas tree,” says Professor Gerland F. Lewis, co-author of the University of Sydney. “On dark nights, you can see the Christmas lights, but not the trees that surround them, but the shape of the lights represents the shape of the tree,” he said. “It’s the same with stellar streams. Their orbits reveal dark matter.”

Astronomers can not only measure velocities, but also use these observations to calculate the chemical composition of a star and find out where the star was born. “The flow of stars can come from destroying galaxies and clusters,” says Professor Alex Zi. University of Chicago, Co-author of the study. “These two types of streams provide different insights into the nature of dark matter.”


Tidal disruption of 10 globular clusters in the Milky Way for 8 billion years. Red particles represent the simulated dark matter of the Milky Way, and green particles represent destructive globular clusters. Stars from destructive globular clusters form a long, orbiting stellar stream. Astronomers use these streams to measure the mass distribution and cohesion of dark matter in the Milky Way, as well as the history of galaxy accretion.Credits: Denis Erkal, S5 Collaboration

According to Professor Lee, these new observations are essential to determine how our Milky Way arose from the featureless universe. big Bang.. “For me, this is one of the most interesting questions, and it’s about our ultimate origin,” Li said. “That’s why we founded S5 and built an international collaboration to deal with it.”

An important factor in the success of the S5 was observations from the Gaia Space Mission in Europe. “Gaia provided us with exquisite measurements of star position and movement that are essential for identifying members of the stellar flow,” said a reader of observational astronomy at the University of Edinburgh and a collaborator in the study. The author, Dr. Sergei Koposov, says.


This was after one globular cluster was torn by the tide for 8 billion years. Red particles represent the dark matter of large galaxies, and green particles represent destructive globular clusters. Due to the influence of the gravity of globular clusters, the stars near the precursor form a characteristic “S” shape.Credits: Denis Erkal, S5 Collaboration

Li’s team plans to generate more measurements in the Milky Way’s stellar stream. Meanwhile, she is happy with these results as a starting point. “In the next decade, there will be a lot of dedicated research on stellar streams,” says Li. “We are the pioneers and pathfinders of this journey. It will be very exciting!”

The results have been approved for publication at the American Astronomical Society. Astrophysical Journal..

See: “S5: Dozen Stella Stream Orbits and Chemists” Ting S. Li, Alexander P. Ji, Andrew B. Pace, Denis Erkal, Sergey E. Koposov, Nora Shipp, Gary S. Da Costa, Lara R. Cullinane, Kyler Kuehn, Geraint F. Lewis, Dougal Mackey, Jeffrey D. Simpson, Daniel B. Zucker, Peter S. Ferguson, Sarah L. Martell, Joss Bland-Hawthorn, Eduardo Balbinot, Kiyan Tavangar, Alex Drlica-Wagner , Gayandhi M. De Silva, Joshua D. Simon, S5 Collaboration, Accepted, Astrophysical Journal..
arXiv: 2110.06950

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