A recent study has shed light on the early evolutionary journey of the Milky Way galaxy, uncovering a significant event that occurred approximately 11.8 billion years ago. Scientists have found evidence indicating that the Milky Way absorbed a smaller galaxy during its formative years when the universe was much younger. This merger represents the earliest known galactic collision for the Milky Way and highlights how the galaxy expanded not only through its own star formation but also by merging with smaller galaxies within its gravitational reach.
The dwarf galaxy involved in this merger was distinct from larger galaxies like the Milky Way and was estimated to contain stars with a mass equivalent to 500 million times that of the sun at the time of the collision. Researchers utilized data from the Hubble and Gaia telescopes to analyze stellar clusters near the Milky Way’s core, studying their age, composition, and trajectory across a region spanning 20,000 light-years from the galaxy’s center.
Following the merger, stars from the dwarf galaxy became integrated into the Milky Way, enriching its stellar population. This event occurred about two billion years after the universe’s inception in the Big Bang. The dwarf galaxy involved in the merger was named Low-energy-Kraken-Heracles (LKH) based on prior studies exploring this primordial collision.
Lead author Davide Massari, an astrophysicist from the National Institute for Astrophysics in Bologna, Italy, emphasized the significance of this discovery, marking the Milky Way’s first merger in its early history. The study suggests that the merger provided the Milky Way with an influx of stars, interstellar gas essential for star formation, and dark matter, contributing to its growth.
While the merger was described as ‘peaceful’ in terms of star interactions, it triggered a significant burst of star formation due to the collision of gases from both galaxies. The study’s findings challenge previous debates on whether the Milky Way’s growth was primarily driven by internal star formation or external mergers.
Furthermore, the Milky Way has been involved in two other major galactic mergers, including the absorption of the Gaia-Sausage-Enceladus dwarf galaxy and ongoing interactions with the Sagittarius dwarf galaxy. These merger events have played a crucial role in shaping the Milky Way’s structure and have impacted the formation of celestial bodies within the galaxy, including our solar system.
Understanding the Milky Way’s historical mergers contributes to unraveling fundamental questions about our cosmic origins and the processes that have shaped our galactic neighborhood.