Twelve for dinner: The Milky Way's feeding habits shine a light on dark
matter

Date:
January 11, 2022
Source:
University of Chicago
Summary:
Astronomers are one step closer to revealing the properties of
dark matter enveloping our Milky Way galaxy, thanks to a new map
of twelve streams of stars orbiting within our galactic halo.



FULL STORY ========================================================================== [Milky Way (stock | Credit: (c) sripfoto / stock.adobe.com] Milky Way
(stock image).

Credit: (c) sripfoto / stock.adobe.com [Milky Way (stock | Credit:
(c) sripfoto / stock.adobe.com] Milky Way (stock image).

Credit: (c) sripfoto / stock.adobe.com Close Astronomers are one step
closer to revealing the properties of dark matter enveloping our Milky
Way galaxy, thanks to a new map of twelve streams of stars orbiting
within our galactic halo.


========================================================================== Understanding these star streams is very important for astronomers. As
well as revealing the dark matter that holds the stars in their orbits,
they also tell us about the formation history of the Milky Way, revealing
that the Milky Way has steadily grown over billions of years by shredding
and consuming smaller stellar systems.

"We are seeing these streams being disrupted by the Milky Way's
gravitational pull, and eventually becoming part of the Milky Way. This
study gives us a snapshot of the Milky Way's feeding habits, such as
what kinds of smaller stellar systems it 'eats'. As our galaxy is getting older, it is getting fatter," said University of Toronto Professor Ting
Li, the lead author of the paper.

Prof. Li and her international team of collaborators initiated a dedicated program -- the Southern Stellar Stream Spectroscopic Survey (S5) --
to measure the properties of stellar streams: the shredded remains of neighboring small galaxies and star clusters that are being torn apart
by our own Milky Way.

Li and her team are the first group of scientists to study such a rich collection of stellar streams, measuring the speeds of stars using
the Anglo- Australian Telescope (AAT), a 4-meter optical telescope in Australia. Li and her team used the Doppler shift of light -- the same
property used by radar guns to catch speeding drivers -- to find out
how fast individual stars are moving.

Unlike previous studies that have focused on one stream at a time,
"S5 is dedicated to measuring as many streams as possible, which we can
do very efficiently with the unique capabilities of the AAT," comments co-author Professor Daniel Zucker of Macquarie University.

The properties of stellar streams reveal the presence of the invisible
dark matter of the Milky Way. "Think of a Christmas tree," says co-author Professor Geraint F. Lewis of the University of Sydney. "On a dark
night, we see the Christmas lights, but not the tree they are wrapped
around. But the shape of the lights reveals the shape of the tree,"
he said. "It is the same with stellar streams -- their orbits reveal
the dark matter." As well as measuring their speeds, the astronomers
can use these observations to work out the chemical compositions of
the stars, telling us where they were born. "Stellar streams can come
either from disrupting galaxies or star clusters," says Professor Alex
Ji at the University of Chicago, a co-author on the study. "These two
types of streams provide different insights into the nature of dark
matter." According to Prof. Li, these new observations are essential for determining how our Milky Way arose from the featureless universe after
the Big Bang. "For me, this is one of the most intriguing questions,
a question about our ultimate origins," Li said. "It is the reason why
we founded S5 and built an international collaboration to address this."
A crucial ingredient for the success of S5 were observations from the
European Gaia space mission. "Gaia provided us with exquisite measurements
of positions and motions of stars, essential for identifying members of
the stellar streams," says Dr. Sergey Koposov, reader in observational astronomy in the University of Edinburgh and a co-author of the study.

Li's team plans to produce more measurements on stellar streams in
the Milky Way. In the meantime, she is pleased with these results as a
starting point.

"Over the next decade, there will be a lot of dedicated studies
looking at stellar streams," Li says. "We are trail-blazers
and pathfinders on this journey. It is going to be very exciting!" ========================================================================== Story Source: Materials provided by University_of_Chicago. Note: Content
may be edited for style and length.


========================================================================== Related Multimedia:
*
Artist's_representation_of_the_Milky_Way_surrounded_by_dozens_of_stellar
streams ========================================================================== Journal Reference:
1. 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. S5: The Orbital
and Chemical Properties of One Dozen Stellar Streams. Astrophysical
Journal, 2022 (accepted); [abstract] ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2022/01/220111153711.htm

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