(ORDO NEWS) — Astronomers know that galaxies grow over time by merging with other galaxies. We can see this happening in our galaxy.
The Milky Way is slowly engulfing the Large and Small Magellanic Clouds and the dwarf spheroidal galaxy Sagittarius.
For the first time, astronomers have discovered evidence of an ancient mass migration of stars into another galaxy.
They have discovered over 7,000 stars in our nearest neighbor, Andromeda (M31). These stars entered the galaxy about two billion years ago.
“Galaxies like M31 and our own Milky Way are built from the building blocks of many smaller galaxies throughout cosmic history,” astrophysicist Arjun Dey, NOIRLab.
New observations of Andromeda and the internal migration of stars come from the Dark Energy Spectroscopic Instrument (DESI), which was created to measure the effect of dark energy on the expansion of the Universe.
The results of the study are presented in a new paper entitled “DESI Observations of the Andromeda Galaxy: Uncovering the Immigration History of Our Nearest Neighbor.”
DESI shows that another galaxy merged with Andromeda about two billion years ago. The positions and movements of about 7500 stars measured by DESI show that they came from another galaxy.
Scientists believe this is how Andromeda and other galaxies became so massive, but now there is more and more clear evidence.
The Milky Way experienced a similar merger 8 to 10 billion years ago. Most of the stars in our galaxy’s halo originated in another galaxy and joined the Milky Way in an ancient merger.
“We’ve never seen this so clearly in the movement of stars before, and we haven’t seen some of the structures that result from this merger,” said astrophysicist Sergei Koposov of the University of Edinburgh and co-author of the paper.
“Our emerging picture is that the history of the Andromeda galaxy is similar to the history of our galaxy.
The inner halos of both galaxies are dominated by a single immigration event.”
For the first time we get an idea about the structures formed as a result of the merger.
“Signs of galaxy migration include debris flows, shells, rings, and plumes, expected outcomes of merging interactions between large galaxies and their companions,” the authors write in their paper.
The study highlights the similarities between Andromeda and the Milky Way , reinforcing the theoretical idea that mergers play a key role in the evolution and growth of galaxies.
The results of the study were obtained thanks to the ability of DESI to collect spectra from 5000 objects simultaneously.
This sophisticated instrument is the most powerful multi-objective spectrograph in the world and can reconfigure its 5,000 individual focal planes in just two minutes while switching between targets.
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