The Andromeda galaxy (Messier 31), which is located 2.5 million light-years away, is the Milky Way’s nearest large galactic neighbor. By measuring the motions of 7,438 stars in the Andromeda’s inner halo, astronomers 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 the Andromeda 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,” said Dr. Arjun Dey, an astronomer at NSF’s NOIRLab.
“Although the night sky may seem unchanging, the Universe is a dynamic place.”
“Galaxies like the Andromeda and our Milky Way are constructed from the building blocks of many smaller galaxies over cosmic history.”
“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,” added Dr. Sergey Koposov, an astrophysicist at the University of Edinburgh.
“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.”
Most of the stars in the Milky Way’s halo were formed in another galaxy and later migrated into our own in a galactic merger 8-10 billion years ago.
Studying the relics of a similar, but more recent, galaxy merger in the Andromeda galaxy gives astronomers a window onto one of the major events in the Milky Way’s past.
To trace the history of migration in the Andromeda, the study authors turned to the Dark Energy Spectroscopic Instrument (DESI) on the Nicholas U. Mayall 4-m telescope at Kitt Peak National Observatory.
DESI was constructed to map tens of millions of galaxies and quasars in the nearby Universe in order to measure…
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