A recent study reveals a significant event in the history of the Milky Way galaxy, shedding light on its growth over time. Approximately 11.8 billion years ago, when the universe was still young, the Milky Way absorbed a smaller dwarf galaxy. This marked the earliest known galactic merger for our galaxy, showcasing how it expanded not only by creating its own stars but also by merging with smaller galaxies within its gravitational reach.
Scientists used the Hubble and Gaia telescopes to examine clusters of stars near the Milky Way’s core, determining the characteristics of these stars and their origins. The dwarf galaxy that merged with the Milky Way, named Low-energy-Kraken-Heracles (LKH), was estimated to contain stars equivalent to 500 million times the mass of the sun at that time, about a quarter of the Milky Way’s size.
The merger added a significant number of stars and interstellar gas to the Milky Way, fueling star formation and contributing to the presence of dark matter. While the merger was peaceful in terms of star interactions, it triggered an explosive collision between gases from the two galaxies, leading to the formation of numerous stars.
The Milky Way has been involved in other galactic mergers in its history, including with the Gaia-Sausage-Enceladus dwarf galaxy and the ongoing merger with the Sagittarius dwarf galaxy. Each merger has impacted the evolution of the Milky Way and played a role in the formation of our solar system and Earth.
Understanding the Milky Way’s past through these mergers helps answer fundamental questions about our origins and the development of our galaxy.