A newly published study sheds light on the complex evolution of the Milky Way galaxy, home to billions of stars, including our sun. Researchers have uncovered evidence of a significant event in the Milky Way’s early history, revealing that the galaxy absorbed a smaller dwarf galaxy approximately 11.8 billion years ago. This merger marked the Milky Way’s earliest-known galactic interaction, demonstrating how the galaxy not only formed its own stars but also grew by merging with smaller galaxies within its gravitational influence.
The dwarf galaxy involved in the merger, named Low-energy-Kraken-Heracles (LKH), was estimated to have contained stars with a mass equivalent to 500 million times that of the sun at the time of the merger, making it about a quarter of the Milky Way’s size. The researchers utilized data from the Hubble and Gaia telescopes to analyze stellar clusters near the Milky Way’s core, investigating their age, chemical composition, and trajectory across a region spanning 20,000 light-years from the galaxy’s center.
According to lead author Davide Massari, astrophysicist at the National Institute for Astrophysics in Bologna, Italy, this study’s key finding is the identification of the Milky Way’s first merger event during its early stages. The research suggests that the merger injected a significant amount of stars, interstellar gas, and dark matter into the Milky Way, fueling star formation in the galaxy’s history.
Massari noted that while the merger was relatively peaceful in terms of star interactions, the collision of gas from the dwarf galaxy likely triggered intense star formation within the Milky Way. The study also revealed that remnants of stars from the dwarf galaxy are likely still present within the Milky Way’s inner regions, although identifying them is challenging due to the high levels of interstellar dust in those areas.
In addition to the LKH merger, the Milky Way has experienced two other major galactic mergers in its history. It assimilated the Gaia-Sausage-Enceladus dwarf galaxy around 1.8 billion years after the LKH merger and has been merging with the Sagittarius dwarf galaxy over the past six billion years. Massari emphasized the impact of these mergers on the formation of our solar system and the Earth, highlighting the importance of understanding the Milky Way’s history in unraveling fundamental questions about our origins.