Recent research has shed light on the tumultuous history of the Milky Way, a vast spiral galaxy hosting billions of stars, including our sun. Scientists have uncovered evidence of a major event in the galaxy’s early days, revealing that around 11.8 billion years ago, when the universe was relatively young, the Milky Way absorbed a smaller galaxy. This marked the earliest known galactic merger for our galaxy, demonstrating its growth not only through internal star formation but also through the incorporation of smaller galaxies drawn in by its gravitational pull.
The assimilated galaxy was classified as a dwarf galaxy, distinct from larger counterparts like the Milky Way. Researchers estimate that it contained stars with a collective mass equivalent to 500 million times that of the sun at the time of the merger, roughly a quarter of the Milky Way’s size during that era.
Utilizing data from the Hubble and Gaia telescopes, scientists analyzed stellar clusters within the Milky Way’s inner 20,000 light-years. By studying the age, chemical composition, and trajectory of these stars, it was confirmed that they originated from a galactic merger occurring approximately two billion years after the universe’s Big Bang event. The dwarf galaxy involved in the merger was named Low-energy-Kraken-Heracles (LKH) in reference to previous studies suggesting such a primordial collision.
Astrophysicist Davide Massari, lead author of the study published in Nature Astronomy, emphasized the significance of this finding, stating that it represents the first merger event experienced by the Milky Way in its formative stages.
The debate over whether the Milky Way’s early development stemmed from internal star formation or galactic mergers has been ongoing. The latest study suggests that the merger injected a substantial number of stars and interstellar gas into the Milky Way, fueling star formation and introducing dark matter into the system.
While the merger was relatively peaceful in terms of star interactions, it triggered a more dynamic interaction between the gas components of the two galaxies, likely leading to heightened star formation, according to Massari.
The Milky Way has been involved in two other significant galactic mergers in its history. Following the LKH merger, it absorbed the Gaia-Sausage-Enceladus dwarf galaxy about 1.8 billion years later, and in the subsequent six billion years, it has been merging with the Sagittarius dwarf galaxy.
Massari emphasized the profound impact of these mergers on the formation of our solar system and Earth, highlighting the importance of understanding the Milky Way’s past in unraveling the origins of our existence.