A recently conducted study has shed light on the long and complex evolution of the Milky Way galaxy, which is a vast spiral galaxy hosting countless stars, including our sun. Researchers studying star clusters near the Milky Way’s center have uncovered evidence of a significant event from over 11.8 billion years ago when a smaller galaxy was absorbed by our galaxy. This marks the earliest known galactic merger for the Milky Way and highlights how the galaxy expanded not only by producing its own stars but also by assimilating smaller galaxies within its gravitational influence.
The smaller galaxy involved in the merger was classified as a dwarf galaxy, distinguishing it from larger galaxies like the Milky Way. Scientists estimate that this dwarf galaxy contained stars with a mass equivalent to 500 million times that of the sun at the time of the merger, approximately one-fourth the size of the Milky Way at that time.
Utilizing data from the Hubble and Gaia telescopes, researchers examined stellar clusters within the innermost 20,000 light-years of the Milky Way. By analyzing the age, chemical composition, and trajectory of these star clusters, they determined that these stars became part of the Milky Way following a galactic merger around two billion years after the Big Bang.
Lead author Davide Massari, an astrophysicist from the National Institute for Astrophysics in Bologna, Italy, emphasized that this discovery represents the first merger event experienced by the Milky Way during its early stages. The study published in the journal Nature Astronomy elucidates that the early growth of the Milky Way was influenced by a peaceful merger with a smaller galaxy, which introduced a significant number of stars, interstellar gas, and dark matter to fuel ongoing star formation.
The merger between the Milky Way and the dwarf galaxy, named Low-energy-Kraken-Heracles (LKH), played a crucial role in shaping the galaxy’s development. This event infused the Milky Way with new stellar material and triggered the formation of numerous stars. Massari explained that while the merger was peaceful in terms of star interactions, it was more explosive regarding the collision of gas from the two galaxies, catalyzing star formation processes.
The Milky Way has also been involved in two other major galactic mergers in its history. It assimilated the Gaia-Sausage-Enceladus dwarf galaxy about 1.8 billion years after the LKH merger and has been gradually merging with the Sagittarius dwarf galaxy over the past six billion years. Massari highlighted the profound impact of these mergers on the formation of our solar system and Earth, emphasizing the importance of understanding the Milky Way’s past in addressing fundamental questions about our origins.