A new study sheds light on the Milky Way galaxy’s history, revealing that it merged with a smaller galaxy approximately 11.8 billion years ago. This merger was a significant event in the Milky Way’s early development, demonstrating how the galaxy evolved not only by creating its own stars but also by incorporating stars from smaller galaxies.
The smaller galaxy involved in the merger was a dwarf galaxy, distinct from larger galaxies like the Milky Way. Researchers estimate that it contained stars with a 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.
Using data from the Hubble and Gaia telescopes, scientists studied stellar clusters within the innermost 20,000 light-years of the Milky Way. These clusters, each housing hundreds of thousands of stars, were analyzed for their age, chemical composition, and trajectory, providing insights into the galaxy’s past.
The merger, which occurred roughly two billion years after the Big Bang, introduced stars from the dwarf galaxy, now named Low-energy-Kraken-Heracles (LKH), into the Milky Way. This discovery represents the earliest-known galactic merger experienced by our galaxy.
Astrophysicist Davide Massari, the lead author of the study published in Nature Astronomy, highlighted the significance of this finding, emphasizing that the merger played a crucial role in the Milky Way’s growth by introducing a substantial volume of stars, interstellar gas, and dark matter.
While the merger was deemed “peaceful” in terms of star interactions, it triggered the formation of numerous stars by combining gases from both galaxies. The Milky Way has been involved in two other major mergers, including the absorption of 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, underscoring the importance of reconstructing the Milky Way’s past to unravel the mysteries of our origins.