What ingredients went into the galactic blender to create the Milky Way?
Our galaxy is a giant `smoothie' of blended stars and gas but a new study tells us where the components came from

Date:
February 22, 2022
Source:
ARC Centre of Excellence for All Sky Astrophysics in 3D (ASTRO 3D)
Summary:
In its early days, the Milky Way was like a giant smoothie, as if
galaxies consisting of billions of stars, and an enormous amount
of gas had been thrown together into a gigantic blender. But a
new study picks apart this mixture by analyzing individual stars
to identify which originated inside the galaxy and which began
'life' outside.



FULL STORY ==========================================================================
In its early days, the Milky Way was like a giant smoothie, as if galaxies consisting of billions of stars, and an enormous amount of gas had been
thrown together into a gigantic blender. But a new study picks apart
this mixture by analysing individual stars to identify which originated
inside the galaxy and which began life outside.


========================================================================== "Although the Milky Way is our home galaxy, we still do not understand
how it formed and evolved," says researcher Sven Buder from the ARC
Centre of Excellence for All Sky Astrophysics in 3 Dimensions (ASTRO 3D)
and the Australian National University (ANU).

His paper, published this week in the Monthly Notices of the Royal
Astronomical Society, analyses the light from stars in detail, helping
to understand what elements went into the creation of the Milky Way we
know today.

"The Milky Way ate up lots of smaller galaxies but, until recently, we did
not have enough evidence of that to say for sure," Buder says. "That's
because simple images of stars in our Milky Way look the same --
whether they were born inside the galaxy or outside and then blended
into the galaxy." Buder and colleagues in the Galactic Archaeology
with HERMES (GALAH) team used Australia's largest optical telescope, the Anglo-Australian Telescope (AAT), at Siding Spring Observatory to split
light from more than 600,000 stars into wavelengths with the HERMES (High Efficiency and Resolution Multi-Element Spectrograph) instrument. This effectively creates 600,000 stellar rainbows known as spectra. Within
each of these rainbows are specific bands of light - - rather like tiny
unique barcodes -- that vary depending on a star's chemical composition.

"If an image is worth a thousand words, these spectra are worth more than
a thousand pictures," says Buder. "By 'scanning' these stellar barcodes,
we measured how abundant 30 elements, such as sodium, iron, magnesium,
and manganese, were, and how they appeared in different concentrations depending on where the star was born." This discovery is an early
step towards reconstructing a picture of the "childhood" of the Milky
Way to get an idea of the size of the galaxies that it consumed in the
process. "It could also help us understand how several of the features
of the galaxy we know today came into being," says Buder.

One mystery the new observations could help solved is why there are
two distinct groups of stars in the disc that we see as the "milky"
band in the night sky.

"The Milky Way spread out across the night sky is a familiar sight,
and when we look at it, we are actually gazing into the centre of our
galaxy with its billions of stars," says Buder. "But we are looking at two populations of stars, one much older than the other. The old stars have
moved so they look like they bulge out of the main plane of the Milky Way, while the younger stars form a much thinner band in the plane. "But we
don't know why this has happened and our latest findings of the remnants
of gigantic, galactic collisions may help us understand," says Buder.

Buder's paper provides the latest revelations relying on data
from the Gaia project -- an ambitious satellite mission to chart a three-dimensional map of the Milky Way to help understand its orbits, composition, formation, and evolution. The Gaia satellite measurements
can help us to find candidates of previously extragalactic stars,
because they still move differently from a typical Milky Way star. But
the extragalactic origin of a star can only be confirmed by its chemical fingerprint.

========================================================================== Story Source: Materials provided
by ARC_Centre_of_Excellence_for_All_Sky_Astrophysics_in_3D_
(ASTRO_3D). Note: Content may be edited for style and length.


========================================================================== Journal Reference:
1. Sven Buder, Karin Lind, Melissa K Ness, Diane K Feuillet, Danny
Horta,
Stephanie Monty, Tobias Buck, Thomas Nordlander, Joss
Bland-Hawthorn, Andrew R Casey, Gayandhi M De Silva, Valentina
D'Orazi, Ken C Freeman, Michael R Hayden, Janez Kos, Sarah L
Martell, Geraint F Lewis, Jane Lin, Katharine J Schlesinger,
Sanjib Sharma, Jeffrey D Simpson, Dennis Stello, Daniel B Zucker,
Tomaž Zwitter, Ioana Ciucă, Jonathan Horner, Chiaki
Kobayashi, Yuan-Sen Ting (丁源森), Rosemary F G
Wyse. The GALAH Survey: chemical tagging and chrono-chemodynamics
of accreted halo stars with GALAH DR3 and Gaia eDR3. Monthly
Notices of the Royal Astronomical Society, 2022; 510 (2): 2407 DOI:
10.1093/mnras/ stab3504 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2022/02/220222135246.htm

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