A recent study has revealed a significant milestone in the history of the Milky Way galaxy. Scientists investigating star clusters near the galactic center have uncovered evidence of a galactic merger that occurred approximately 11.8 billion years ago, when the universe was still in its early stages. This event marks the earliest-known merger experienced by the Milky Way, highlighting its growth not only through internal star formation but also through the assimilation of smaller galaxies within its gravitational influence.
The merging galaxy, classified as a dwarf galaxy, was estimated to possess 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. Researchers utilized data from the Hubble and Gaia telescopes to analyze stellar clusters within the Milky Way’s innermost 20,000 light-years, studying their age, chemical composition, and trajectory.
The merger, which occurred roughly two billion years after the Big Bang, introduced stars and interstellar gas to the Milky Way, fueling star formation and contributing dark matter. Lead author Davide Massari emphasized the peaceful nature of the merger concerning stars, with no star-to-star collisions, while acknowledging a more explosive interaction between the gas from both galaxies, likely triggering the formation of numerous stars.
Massari suggested that numerous stars originating from the dwarf galaxy may still reside within the Milky Way, particularly within stellar clusters in the inner regions. The Milky Way has undergone two other significant galactic mergers, absorbing the Gaia-Sausage-Enceladus dwarf galaxy and currently merging with the Sagittarius dwarf galaxy. Massari emphasized the impact of these mergers on the formation of our solar system and the Earth, highlighting the importance of understanding the Milky Way’s history in answering fundamental questions about our origins.