A recent study has unveiled a significant event in the history of the Milky Way galaxy, shedding light on its early development. Scientists analyzing star clusters near the galactic center have found evidence suggesting that the Milky Way consumed a smaller galaxy around 11.8 billion years ago, during a time when the universe was much younger. This marks the earliest known galactic merger for our galaxy and highlights how it expanded not just by creating its own stars but also by merging with smaller galaxies pulled into its gravitational field.
The consumed galaxy, classified 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 time. Researchers utilized the Hubble and Gaia telescopes to examine stellar clusters within the innermost 20,000 light-years of the Milky Way, analyzing their age, chemical makeup, and trajectory. One light-year equals the distance light travels in a year, approximately 9.5 trillion kilometers.
These stars became part of the Milky Way following a galactic merger that occurred roughly two billion years after the Big Bang. The dwarf galaxy, known as Low-energy-Kraken-Heracles (LKH), was the origin of these stars, a name derived from previous studies exploring this primordial merger possibility.
Astrophysicist Davide Massari, the lead author of the study published in Nature Astronomy, emphasized the significance of this research in unveiling the galaxy’s early merger event. The study indicates that the merger introduced a substantial number of stars, interstellar gas, and dark matter to the Milky Way, fueling star formation.
Massari explained that while the merger was relatively peaceful in terms of star interactions, it triggered the formation of numerous stars due to the collision of gases from the two galaxies. He also mentioned the difficulty in identifying individual stars within the Milky Way’s inner regions due to the abundance of interstellar dust.
The Milky Way has been involved in two other major galactic mergers, including one with the Gaia-Sausage-Enceladus dwarf galaxy and ongoing interactions with the Sagittarius dwarf galaxy over the past six billion years. Massari highlighted the impact of these mergers on the formation of our solar system and Earth, emphasizing the importance of understanding the galaxy’s history in answering fundamental questions about our origins.
