- 3934 - DESI - galaxies grow by merging? Astronomers know that galaxies grow over time through mergers with other galaxies. We can see it happening in our galaxy. The Milky Way is slowly absorbing the Large and Small Magellanic Clouds and the Sagittarius Dwarf Spheroidal Galaxy.
------------------ 3934
- DESI -
galaxies grow by merging?
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- Astronomers
have found evidence of an ancient mass migration of stars into another galaxy.
They spotted over 7,000 stars in Andromeda (M31), our nearest neighbour, that
merged into the galaxy about two billion years ago.
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- One of the
James Webb Telescopes's main scientific objectives is to look back in time to
the Universe’s earliest galaxies to understand how they’ve grown and evolved
into what they are today.
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- Galaxies
like M31 and our Milky Way are constructed from the building blocks of many
smaller galaxies over cosmic history.
These new observations of Andromeda and the inward migration of stars
comes from the Dark Energy Spectroscopic Instrument (DESI.)
-
- DESI was
built to measure the effect dark energy has on the expansion of the
Universe. DESI does that by gathering
optical spectra on tens of millions of objects, mostly galaxies and quasars,
and then constructing a 3D map of the results.
-
- DESI is
similar to the more well-known “Gaia spacecraft”. Gaia has an ambitious goal to
precisely map the positions and motions of billions of stars in the Milky Way.
Gaia data led to a wealth of discoveries about our own galaxy. But it’s
confined to mapping stars in the Milky Way.
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- Now, thanks
to DESI, astronomers have at least a partial map of the stars in Andromeda for
the first time. And that map, including the motions of nearly 7,500 stars in
the inner halo of the Andromeda Galaxy, is revealing their history.
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- DESI shows
that about two billion years ago, another galaxy merged with Andromeda. The
positions and motions of about 7,500 stars DESI measured reveal that they came
from another galaxy.
-
- Our new
observations of the Milky Way’s nearest large galactic neighbor, the Andromeda
Galaxy, reveal evidence of a galactic immigration event in exquisite
detail. Although the night sky may seem
unchanging, the Universe is a dynamic place. Galaxies like M31 and our Milky
Way are constructed from the building blocks of many smaller galaxies over
cosmic history.
-
- The Milky
Way experienced a similar merger between 8 to 10 billion years ago. Most of the
stars in our galaxy’s halo originated in a different galaxy and joined the
Milky Way as a result of the ancient merger. Astronomers can learn more about
the Milky Way’s ancient history by closely observing this similar, more recent
merger event in Andromeda.
-
- The
expected observational signatures of galactic migration include debris streams,
shells, rings, and plumes, the expected outcomes of merger interactions between
large galaxies and their companions.
-
- The results
are consistent with the interpretation that much of the substructure in the
inner halo of M31 is produced by a single galactic immigration event 1–2
billion years ago.
-
- The new
observations reveal intricate coherent kinematic structure in the positions and
velocities of individual stars: streams, wedges, and chevrons. Though the
positions and velocities of the 7,500 stars play a major role in these
findings, so did stellar metallicity.
-
- The
observastions found high-metallicity stars in all of the sub-structures
stemming from the merger. A significant
numbers of metal-rich stars across all of the detected substructures, suggests
that the progenitor galaxies had an extended star formation history, one
perhaps more representative of more massive galaxies.
-
- M31 is
remarkably similar to the Milky Way in that the inner halos of both galaxies
are dominated by stars from a single accretion event. DESI’s power is on full display in this
research. The results stem from DESI’s ability to gather spectra from 5,000
objects simultaneously.
-
- This
complex instrument is the most powerful multi-object survey spectrograph in the
world and can reconfigure its 5,000 separate focal planes in only two minutes
as it slews between targets. It’s
amazing that we can look out at the sky and read billions of years of another
galaxy’s history as written in the motions of its stars.”
-
- It was
designed to measure the spectra of over 40 billion distant galaxies and quasars
to map the large-scale structure of the Universe and how dark energy fuels its
expansion. Along the way, it’s showing us how galaxies merge over time.
-
- We can look
out at the sky and read billions of years of another galaxy’s history as
written in the motions of its stars, each star tells part of the story.
-
- Over the
course of billions of years, galaxies grow and evolve by forging new stars and
merging with other galaxies through aptly named “galactic immigration” events.
-
- By
measuring the motions of nearly 7,500 stars in the inner halo of the Andromeda
Galaxy, also known as Messier 31 (M31), the team discovered telltale patterns
in the positions and motions of stars that revealed how these stars began their
lives as part of another galaxy that merged with M31 about 2 billion years ago.
-
- New
observations of the Milky Way’s nearest large galactic neighbor, the Andromeda
Galaxy, reveal evidence of a galactic immigration event in exquisite
detail. Although the night sky may seem
unchanging, the Universe is a dynamic place. Galaxies like M31 and our Milky
Way are constructed from the building blocks of many smaller galaxies over
cosmic history.
-
- Our emerging
picture is that the history of the Andromeda Galaxy is similar to that of our
own Galaxy, the Milky Way. The inner halos of both galaxies are dominated by a
single immigration event.
-
- DESI was
constructed to map tens of millions of galaxies and quasars in the nearby
Universe in order to measure the effect of dark energy on the expansion of the
Universe.
-
- It is the
most powerful multi-object survey spectrograph in the world, and is capable of
measuring the spectra of more than 100,000 galaxies a night.
-
- Even though
the “Mayall Telescope” was completed 50 years ago (it achieved first light in
1973), it remains a world-class astronomical facility thanks to continued
upgrades and state-of-the-art instrumentation.
With renewal and reuse, a venerable telescope like the Mayall can
continue to make amazing discoveries despite being relatively small by today’s
standards.
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March 27, 2023 DESI - galaxies grpw by merging? 3934
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--- Wednesday, March 29, 2023 ---------------------------
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