Astronomers Detect a Mass Migration of Stars Converging on Andromeda

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.