Astronomers measured the movements of more than 7,500 stars inhabiting the innermost halo of M31. Scientists discovered conclusive telltale signs of positions and motions that suggest some of the stars did not form in Andromeda but were stars from another galaxy that merged with M31 around 2 billion years ago.
The closest galaxy to the Milky Way is M31, also known as the Andromeda galaxy. With an approximate diameter of 152,000 light-years, this neighboring galaxy is expected to collide with the Milky Way somewhere between 4 to 5 billion years from now. Once the collision occurs, it will produce one massive elliptical or lenticular galaxy. But it seems that Andromeda is no stranger to collisions, as astronomers believe that fragments of much smaller galaxies are embedded within its center. Now, astronomers have discovered new evidence that suggests a large galactic migration event of stars towards Andromeda, the closest neighboring galaxy to the Milky Way. So while the night sky we observe and photograph might seem as if it is not changing, the universe we live in is highly dynamic.
Mass-migration of stars
Astronomers measured the movements of more than 7,500 stars inhabiting the innermost halo of M31. Scientists discovered conclusive telltale signs of positions and motions that suggest some of the stars did not form in Andromeda but were stars from another galaxy that merged with M31 around 2 billion years ago. Scientists have long predicted and theorized these collisions and patterns, but experts have never found such conclusive evidence. The new data was obtained using the DOE’s Dark Energy Spectroscopic Instrument on the Nicholas U. Mayall 4-meter Telescope at Kitt Peak National Observatory, Arizona.
The Andromeda and the Milky Way Galaxy are not that dissimilar
As explained by Arjun Dey, a NORILab astronomer, these observations offer evidence of a galactic mass migration event in exquisite detail. “Galaxies like M31 and our Milky Way are built from the building blocks of many smaller galaxies throughout cosmic history,” Dey explained in a statement. Scientists stress that never before have they been able to see so clearly the movement of stars, nor have they been able to take a peak at some of the structures that resulted from such cosmic fusions. Furthermore, such data can tell us much about our galaxy and its similarity with Andromeda. Based on this data, the two galaxies are very similar. The researchers have revealed that similar mass migrations dominate the outer halos of both galaxies. In other words, the study offers tantalizing clues about our cosmic neighbors and the history of our own galaxy. Scientists believe that many of the stars that reside in the outer halo of the Milky Way galaxy were birthed in other galaxies but eventually migrated to the Milky Way in a galactic fusion that is thought to have taken place between 8 and 10 million years ago.
A research paper detailing the discovery appears in The Astrophysical Journal.
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