- 3881 - ANDROMEDA GALAXY - next door neighbor Astronomers have discovered new evidence that Andromeda, the galaxy next door to our own, grew by merging with another galaxy. The event triggered a mass migration of stars into the galaxy
--------------- 3881 - ANDROMEDA GALAXY - next door neighbor
- The evidence
of the mergers came in the form of observations of the individual motions of
almost 7,500 stars in the inner halo of Andromeda. This showed these stars had
begun their lives as part of another galaxy that merged with Andromeda around 2
billion years ago.
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- 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.
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- The majority
of the stars in the Milky Way's halo are also believed to have originated in
another galaxy finding a new galactic home during a massive merger event that
occurred between 8 to 10 billion years ago.
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- To trace
stellar migration in the galaxy, the team turned to “DESI” due to the fact that
it is the most powerful multi-object survey spectrograph in the world, capable
of measuring the spectra of more than 100,000 galaxies in a single night.
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- In only a
few hours of observing time, DESI was able to surpass more than a decade of
spectroscopy with much larger telescopes.m
Despite first opening its eye to the universe in 1973, the Mayall
Telescope is still able to play a role in cutting-edge research like this
thanks to five decades of upgrades and improvements.
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- 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.
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- We 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.
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- Galaxies
like M31 and our Milky Way are constructed from the building blocks of many
smaller galaxies over cosmic history.
“Dark Energy Spectroscopic Instrument” (DESI.) was built to measure the
effect dark energy has on the expansion of the Universe. It 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.
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- DESI is
similar to the “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. Theory told us this was how Andromeda and other galaxies
grew so massive, but now there’s a growing body of clear evidence.
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- 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.
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- 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.
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- The team
found high-metallicity stars in all of the sub-structures stemming from the
merger. Significant numbers of
metal-rich stars across all of the detected substructures, suggesting that the
progenitor galaxy (or galaxies) had an extended star formation history.
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- 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.
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- 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.
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February 19, 2023 ANDROMEDA GALAXY
- next door neighbor 3881
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