A recent study has shed light on the complex journey of the Milky Way, a vast spiral galaxy housing billions of stars, including our sun. Researchers have uncovered evidence suggesting that the Milky Way engulfed a smaller galaxy approximately 11.8 billion years ago when the universe was still in its infancy. This marks the earliest known galactic merger for the Milky Way, showcasing its growth not only through internal star formation but also by assimilating smaller galaxies within its gravitational reach.
The smaller galaxy involved in the merger was classified as a dwarf galaxy, containing stars with a mass equivalent to 500 million solar masses at the time of the event, about a quarter of the Milky Way’s size back then. By leveraging data from the Hubble and Gaia telescopes, scientists studied stellar clusters within the Milky Way’s central region, examining their age, chemical makeup, and trajectories spanning 20,000 light-years. Notably, a light-year represents the distance light travels in a year, equivalent to 9.5 trillion kilometers.
Referred to as Low-energy-Kraken-Heracles (LKH), the dwarf galaxy contributed stars to the Milky Way following the merger, which occurred around two billion years after the universe’s inception during the Big Bang event. Lead author Davide Massari, an astrophysicist at the National Institute for Astrophysics in Bologna, Italy, emphasized the significance of this discovery as the earliest merger experienced by the Milky Way.
The study’s findings suggest that the merger injected the Milky Way with a substantial amount of stars, interstellar gas fueling star formation, and dark matter in its early stages. While the merger was deemed peaceful in terms of star collisions, the interaction between gases from LKH and the Milky Way likely triggered a surge in star formation.
Massari highlighted that numerous stars originating from LKH may still reside within the Milky Way’s inner regions, concealed within stellar clusters due to interstellar dust hindering individual star identification. The Milky Way has also been involved in two other significant 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.
According to Massari, each merger has influenced the formation of our solar system and Earth, emphasizing the importance of reconstructing the Milky Way’s history in understanding our cosmic origins.
