- 3912 - GALAXY - history how they are created? 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.
------------ 3912 - GALAXY - history how they are created?
- 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 neighbor, that
merged into the galaxy about two billion years ago.
-
- The James
Webb Space Telescope'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. 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.) It 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.
-
- 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.
-
- DESI has
given astronomers 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.
-
- 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.
-
- 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.
-
- 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.
-
- We find
clear kinematic evidence for shell structures in the Giant Stellar Stream, the
Northeast Shelf and Western Shelf regions.
The kinematics are remarkably similar to the predictions of dynamical
models constructed to explain the spatial morphology of the inner halo. 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.
-
- Though the
positions and velocities of the 7500 stars play a major role in these findings,
so did stellar metallicity. The high-metallicity stars in all of the
sub-structures stemming from the merger. We find significant numbers of
metal-rich stars across all of the detected substructures, suggesting that the
progenitor galaxy had an extended star formation history, one perhaps more
representative of more massive galaxies.
-
- 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 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. In only a few hours of observing time, DESI
was able to surpass more than a decade of spectroscopy with much larger
telescopes.
-
- 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.
Astronomers try to uncover the histories of these immigration events by
studying the motions of individual stars throughout a galaxy and its extended
halo of stars and dark matter. Such cosmic archaeology, however, has only been
possible in our own galaxy, the Milky Way, until now.
-
- 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.
While such patterns have long been predicted by theory, they have never been
seen with such clarity in any galaxy.
-
- To trace
the history of migration in M31, the team turned to DESI. 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.
-
- The team
now plans to use the unparalleled capabilities of DESI and the Mayall Telescope
to explore more of M31’s outlying stars, with the aim of revealing its
structure and immigration history in unprecedented detail.
-
- 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, each star tells part of the
story. Who knows what new discoveries
await!
-
March 10, 2023 GALAXY -
history how they are created? 3912
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--- Saturday, March 11, 2023 ---------------------------
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