The Milky Way, a vast spiral galaxy housing billions of stars, including our sun, has undergone a complex journey to reach its current size, as indicated by recent research highlighting a significant event in its early history.
Scientists studying star clusters near the Milky Way’s core have found evidence suggesting that approximately 11.8 billion years ago, our galaxy absorbed a smaller galaxy when the universe was still very young. This marks the earliest galactic merger known to have involved the Milky Way, demonstrating its growth through not only internal star formation but also the assimilation of smaller galaxies within its gravitational grasp.
The smaller galaxy, categorized as a dwarf galaxy, was estimated to contain stars with a total mass equivalent to 500 million times that of the sun at the time of the merger, making it roughly a quarter of the Milky Way’s size back then.
By utilizing the Hubble and Gaia telescopes, researchers examined stellar clusters within the Milky Way’s innermost 20,000 light-years, analyzing their age, chemical composition, and paths. Each cluster harbors hundreds of thousands of stars that became part of the Milky Way following a galactic merger occurring about two billion years after the Big Bang.
The dwarf galaxy, where these stars originated, was named Low-energy-Kraken-Heracles (LKH) in reference to previous studies exploring the possibility of such a merger.
Lead author Davide Massari, an astrophysicist at the National Institute for Astrophysics in Bologna, Italy, emphasized the discovery of the Milky Way’s earliest merger as a key outcome of the research, shedding light on the galaxy’s formative years.
The study suggests that the Milky Way’s growth was influenced by a combination of internal star formation and galactic mergers, providing the galaxy with a substantial influx of stars, interstellar gas fueling star birth, and dark matter.
According to Massari, the merger process was relatively peaceful for the stars involved, with no star-to-star collisions. However, the collision of gases from the two galaxies likely triggered a surge in star formation.
The Milky Way has experienced two other significant galactic mergers: one with the Gaia-Sausage-Enceladus dwarf galaxy approximately 1.8 billion years after the LKH merger, and another ongoing merger with the Sagittarius dwarf galaxy over the past six billion years.
These mergers have influenced the evolution of the Milky Way, including the development of our solar system and Earth, underscoring the importance of understanding the galaxy’s history in answering fundamental questions about our origins.
