Astronomers Discover Mass Migration of Stars in Andromeda Galaxy

02:44 GMT, 15 February 2023
CC BY 2.0 / andy /
Egor Shapovalov
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Studying the stars is a very demanding process, especially when the events of interest took place centuries ago. However, a team of astrophysicists have been lucky enough to use ultra-modern technology to capture a process in a neighboring galaxy that could reveal details of our galaxy's past.
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An international team of scientists has found new evidence showing a mass migration of celestial bodies migrating from one galaxy to another, marking a first for astronomers.
Astronomers used data from the US Department of Energy's Dark Energy Spectroscopic Instrument (DESI), of the Nicholas U. Mayall four-meter Telescope at the Kitt Peak National Observatory.
Scientists determined their findings after measuring the movements of nearly 7,500 stars in the inner halo of the Andromeda Galaxy, also known as Messier 31 (M31). As a result, astronomers found controlling patterns in the positions and motions of the stars. It turned out that when these stars were born, they were part of another galaxy, and later merged with M31 about 2 billion years ago.

"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," explained lead author Arjun Dey. "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."

Most of the Milky Way's stars formed in another galaxy and migrated in a massive merger between 8 and 10 billion years ago. Thus, studying the remnants of a similar but more recent galaxy merger in M31 may help scientists investigate our galaxy's past.

"We have never before seen this so clearly in the motions of stars, nor had we seen some of the structures that result from this merger," said Sergey Koposov, an astrophysicist at the University of Edinburgh and co-author of the paper. "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."

Scientists also noted that such a survey was only possible thanks to DESI, which was built to map tens of millions of galaxies in the near Universe.
"This science could not have been done at any other facility in the world. DESI's amazing efficiency, throughput, and field of view make it the best system in the world to carry out a survey of the stars in the Andromeda Galaxy," said Dey. "In only a few hours of observing time, DESI was able to surpass more than a decade of spectroscopy with much larger telescopes."
The instrument is still the world's most powerful multi-object survey spectrograph. Among other features, it can measure the spectra of more than 100 000 galaxies overnight.
The paper "DESI Observations of the Andromeda Galaxy: Revealing the Immigration History of our Nearest Neighbor" is available for review on the arXiv and will appear in The Astrophysical Journal.
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