A recent study has shed light on the early history of the Milky Way galaxy, revealing a significant merger event that occurred approximately 11.8 billion years ago, when the universe was still in its infancy. The research, conducted by scientists studying star clusters near the center of the Milky Way, shows evidence of a smaller galaxy being absorbed by our galaxy. This marks the earliest-known galactic merger experienced by the Milky Way, highlighting its growth not just through internal star formation but also by assimilating smaller galaxies within its gravitational influence.
The dwarf galaxy involved in the merger, named Low-energy-Kraken-Heracles (LKH), was estimated to have a mass equivalent to 500 million times that of the sun at the time of the merger, making it about a quarter of the size of the Milky Way during that period. Researchers utilized data from the Hubble and Gaia telescopes to analyze stellar clusters within the innermost 20,000 light-years of the Milky Way, examining their age, composition, and trajectory.
According to lead author Davide Massari, an astrophysicist at the National Institute for Astrophysics in Bologna, Italy, the merger event injected a substantial number of stars and interstellar gas into the early Milky Way, fueling star formation and contributing to the presence of dark matter. While the merger was described as “peaceful” in terms of star interactions, the collision of gases from the two galaxies likely triggered a burst of star formation.
Massari suggested that many stars originating from the dwarf galaxy LKH might still be present within the Milky Way, particularly within stellar clusters in the inner regions. Despite the challenges of identifying individual stars due to interstellar dust, ongoing research indicates that the Milky Way has undergone multiple mergers throughout its history. Apart from the LKH merger, the Milky Way has also merged with the Gaia-Sausage-Enceladus dwarf galaxy and the Sagittarius dwarf galaxy in the past billion years.
Each of these merger events has had a significant impact on the formation of the Milky Way, including the solar system and Earth. Massari emphasized the importance of understanding the galaxy’s past as a means to illuminate humanity’s origins.