Galaxies are known to grow throughout time through mergers with other
galaxies, according to astronomers. In our galaxy, we can observe it taking
place. The Sagittarius Dwarf Spheroidal Galaxy and the Large and Small
Magellanic Clouds are being
steadily absorbed
by the Milky Way.
Astronomers have discovered proof of an ancient star migration in another
galaxy for the first time. In Andromeda (M31), our nearest neighbor, they
discovered nearly 7,000 stars that joined the galaxy roughly two billion
years ago.
Astronomy's current focus on the growth and evolution of galaxies is one of
the factors contributing to the James Webb Space Telescope's recent media
attention. Looking
back in time
to the oldest galaxies in the Universe to understand how they have developed
and evolved into what they are now is one of the key scientific goals of the
JWST. However, it's not the only telescope that may illuminate the
situation.
"Over the course of cosmic history, smaller galaxies like M31 and our Milky Way served as the building blocks for larger galaxies like M31 and our own."NOIRLab, Arjun Dey
The Dark Energy Spectroscopic
Instrument is responsible for these latest studies of Andromeda and the
inward movement of stars (DESI.) It was created to track the impact dark
energy has on the universe's expansion. This is accomplished by collecting
the optical spectra of tens of millions of objects, mostly galaxies and
quasars, and creating a 3D map using the data.
Comparable to the more well-known
Gaia spacecraft
is DESI. The exact mapping of the locations and movements of the Milky Way's
billions of stars is one of Gaia's lofty objectives. We learned a great deal
about our own galaxy thanks to the Gaia data. However, it is only used to
chart stars in the Milky Way.
Astronomers now have, for the first time, at least a partial map of the
stars in Andromeda, courtesy to DESI. And that map, which includes the
movements of roughly 7,500 stars in the Andromeda Galaxy's inner halo, is
illuminating their past.
The new study "DESI Observations of the Andromeda Galaxy: Revealing the
Immigration History of our Nearest Neighbor" contains these findings. Arjun
Dey, an astronomer at NOIRLab, the NSF facility that houses DESI, is the
paper's primary author and it will be published in The Astrophysical
Journal.
According to DESI, Andromeda and another galaxy merged some two billion
years ago. 7,500 stars were measured by DESI, and their locations and
movements show that they originated in a different galaxy. There is a
growing body of convincing data that contradicts the theory that says this
is how Andromeda and other galaxies became so large.
Lead author Dey said, "Our new views of the Andromeda Galaxy, the Milky
Way's nearest massive galactic neighbor, offer evidence of a galactic
immigration event in exquisite detail. "The universe is a dynamic realm even
if the night sky may appear to be static. Over the course of cosmic history,
smaller galaxies like M31 and our Milky Way served as the building blocks
for larger galaxies like M31 and our own."
A comparable merger occurred between 8 and 10 billion years ago in the
Milky Way. The vast majority of the stars in the halo of our galaxy were
born in other galaxies and merged with the Milky Way during the early
merger. By carefully watching this comparable, more recent merger event in
Andromeda, astronomers can understand more about the Milky Way's ancient
past.
According to coauthor Sergey Koposov, an astronomer at the University of
Edinburgh, "we had never seen this so clearly in the movements of stars, nor
have we observed some of the structures that come from this merging." "The
Andromeda Galaxy's history resembles that of the Milky Way, according to the
developing image. A single immigration event dominates both galaxies' inner
halos."
We finally have a peek of the buildings that resulted from the merging. The
debris streams, shells, rings, and plumes that are anticipated to result
from merger encounters between massive galaxies and their partners are among
the predicted observable markers of galactic migration, according to the
authors of the study.
In the Giant Stellar Stream, Northeast Shelf, and Western Shelf sectors,
"we discover convincing kinematic evidence for shell structures," according
to the report. "The kinematics are strikingly consistent with dynamical
models developed to account for the spatial architecture of the inner halo.
The findings support the hypothesis that a significant portion of the
substructure in M31's inner halo was created by a single galactic
immigration event 1-2 Gyr ago."
The authors state in their research, "While signs of coherent structures
had previously been found in M31, this is the first time they have been
spotted with such precision and clarity in a galaxy beyond the Milky Way.
The data show complex coherent kinematic structure, including wedges,
streams, and chevrons, in the locations and velocities of individual
stars.
The 7,500 stars' locations and velocities were important in these
discoveries, but so was stellar metallicity. In each of the sub-structures
resulting from the merger, the scientists discovered stars with high
metallicities. In their conclusion, the scientists state that "we discover
considerable quantities of metal-rich stars throughout all of the identified
substructures, suggesting that the progenitor galaxy (or galaxies) had a
protracted star formation history, one potentially more characteristic of
more massive galaxies."
The study emphasizes the parallels between the Milky Way and Andromeda,
supporting the theory that mergers are essential to galactic history and
expansion. The inner halos of both galaxies are dominated by stars from a
single accretion event, which makes M31 and the Milky Way strikingly
similar, according to the study. In fact, a recent investigation of the
kinematics of Milky Way stars close to the Sun shows kinematic substructures
with chevron shapes that are similar to those described here.
The potency of DESI is amply demonstrated in this study. The outcomes come
from DESI's capacity to concurrently collect spectra from 5,000 objects.
This complicated device can rearrange its 5,000 distinct focus planes in
only two minutes as it slews between targets, making it the most potent
multi-object survey spectrograph in the world.
It's incredible that we can gaze up at the sky and decipher the
star-movements of another galaxy to reveal billions of years of its
past.
NOIRLab's Joan R. Najita
Its goal is to explore the large-scale structure of the Universe and
understand how dark energy drives its expansion by measuring the spectra of
more than 40 billion far-off galaxies and quasars. It is demonstrating to us
how galaxies fuse over time as it goes.
"No other facility in the world could have been used to do this research.
The greatest system in the world for conducting a survey of the stars in the
Andromeda Galaxy is DESI due to its astounding efficiency, throughput, and
field of vision "said Dey. "DESI was able to surpass more than a decade of
spectroscopy with far larger telescopes in only a few hours of observation
time," says the statement.
According to co-author Joan R. Najita, also from NOIRLab, "it's astounding
that we can gaze out into the sky and read billions of years of the history
of another galaxy as recorded in the movements of its stars - each star
tells part of the narrative." "We were pleasantly surprised by our early
discoveries, and we now want to use DESI to study the whole M31 halo. Who
knows what fresh findings are ahead?"
This article was originally published by
Universe Today. Read the
original article.
