A recent study has revealed a significant event from the early history of our galaxy, the Milky Way. Scientists have found evidence indicating that the Milky Way absorbed a smaller galaxy approximately 11.8 billion years ago when the universe was still young. This merger, the earliest known in the Milky Way’s history, highlights how the galaxy has grown not only by forming its own stars but also by merging with smaller galaxies pulled in by its gravitational force.
The smaller galaxy involved in the merger was classified as a dwarf galaxy, distinguishing it from larger galaxies like the Milky Way. Researchers estimate that this dwarf galaxy contained stars with a combined mass equal 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 time.
Utilizing data from the Hubble and Gaia telescopes, researchers studied clusters of stars within the Milky Way’s innermost 20,000 light-years. By analyzing the age, chemical composition, and trajectory of these stars, they traced their origins back to a galactic merger that occurred around two billion years after the Big Bang.
The dwarf galaxy involved in the merger was named Low-energy-Kraken-Heracles (LKH) in reference to earlier studies exploring the possibility of such a primordial merger. Lead author Davide Massari, an astrophysicist from the National Institute for Astrophysics in Bologna, Italy, emphasized the significance of this discovery as the Milky Way’s first merger event during its early stages.
The research suggests that the Milky Way’s growth was influenced by a combination of homegrown star formation and galactic mergers. The merger with the dwarf galaxy infused the Milky Way with stars, interstellar gas, and dark matter, fueling star formation processes. Massari described the merger as relatively peaceful for stars but more explosive for gas, likely triggering a burst of star formation.
The Milky Way has been involved in two other major mergers with galaxies in its history. It absorbed the Gaia-Sausage-Enceladus dwarf galaxy about 1.8 billion years after the LKH merger and has been merging with the Sagittarius dwarf galaxy over the past six billion years. Each of these mergers has shaped the Milky Way’s evolution and influenced the formation of our solar system and Earth.
Understanding the Milky Way’s past through these mergers contributes to answering fundamental questions about our origins and the formation of our galaxy.
