A recent study has shed light on the complex evolution of the Milky Way galaxy, home to billions of stars, including our own sun. Researchers have uncovered evidence of a significant event in the Milky Way’s history, revealing that approximately 11.8 billion years ago, when the universe was much younger, our galaxy absorbed a smaller galaxy. This galactic merger marked an early milestone in the Milky Way’s growth, demonstrating that besides producing its own stars, it expanded by assimilating smaller galaxies within its gravitational influence.
The smaller galaxy involved in the merger was classified as a dwarf galaxy, distinguished from larger galaxies like the Milky Way. Estimates suggest that this dwarf galaxy contained stars with a mass equivalent to 500 million times that of the sun at the time of the merger, roughly a quarter of the Milky Way’s size at that period.
Utilizing data from the Hubble and Gaia telescopes, scientists studied stellar clusters within the Milky Way’s innermost 20,000 light-years to examine their age, chemical composition, and trajectory. These stars became part of the Milky Way following a galactic merger that occurred approximately two billion years after the Big Bang.
Lead author Davide Massari from the National Institute for Astrophysics in Bologna, Italy, emphasized the significance of this discovery, naming the dwarf galaxy involved in the merger as Low-energy-Kraken-Heracles (LKH). The study published in Nature Astronomy marks the first confirmed merger event experienced by the Milky Way during its early stages.
The study suggests that the merger injected a substantial number of stars and interstellar gas into the Milky Way, fueling star formation and contributing to the presence of dark matter. Massari highlighted that while the merger was peaceful in terms of stars, the collision of gases likely triggered the formation of many stars, defining the event as more “explosive” from a gas perspective.
The Milky Way has been part of other significant galactic mergers, including one with the Gaia-Sausage-Enceladus dwarf galaxy and ongoing interactions with the Sagittarius dwarf galaxy. Massari emphasized the impact of these mergers on the formation of our solar system and Earth, emphasizing the importance of understanding the Milky Way’s history in addressing fundamental questions about our origins.