A recent study has shed light on the complex evolution of the Milky Way galaxy, showcasing a significant milestone in its history. Researchers studying star clusters near the galaxy’s core have uncovered evidence of a galactic merger that occurred approximately 11.8 billion years ago, during the universe’s early stages. This event marks the earliest-known merger experienced by the Milky Way, highlighting how the galaxy expanded not only through internal star formation but also by assimilating smaller galaxies within its gravitational reach.
The merging galaxy, identified as a dwarf galaxy, was estimated to contain stars with a mass equivalent to 500 million times that of the sun at the time of the merger, making it about a quarter of the Milky Way’s size at that period. By utilizing data from the Hubble and Gaia telescopes, researchers analyzed stellar clusters within the Milky Way’s innermost 20,000 light-years, examining their age, chemical composition, and trajectory.
The study revealed that these stars, originating from a dwarf galaxy named Low-energy-Kraken-Heracles (LKH), became part of the Milky Way following the merger, which occurred roughly two billion years after the Big Bang. Lead author Davide Massari emphasized the significance of this discovery, describing it as the first merger event experienced by the Milky Way during its infancy.
The research suggests that the merger injected the Milky Way with a substantial volume of stars, interstellar gas, and dark matter early in its history, fueling star formation. Massari noted that while the merger was relatively peaceful in terms of star interactions, it triggered the formation of numerous stars through the collision of gases from LKH and the Milky Way.
Furthermore, the Milky Way has been involved in two other major galactic mergers, including the absorption of Gaia-Sausage-Enceladus and ongoing interactions with the Sagittarius dwarf galaxy. Massari emphasized the impact of these mergers on the formation of our solar system and Earth, highlighting the importance of understanding the galaxy’s past in answering fundamental questions about our origins.