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 detailed by recent research highlighting a significant event in its early history.
Scientists studying star clusters near the center of the Milky Way have uncovered proof that our galaxy absorbed a smaller galaxy approximately 11.8 billion years ago, when the universe was still young. This event marks the earliest galactic merger known to have occurred in the Milky Way’s past, demonstrating its growth through not only internal star formation but also the assimilation of smaller galaxies through gravitational attraction.
The smaller galaxy involved in the merger was categorized as a dwarf galaxy, distinguishing it from larger galaxies like the Milky Way. Researchers estimate it contained stars with a 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 at the time.
Utilizing data from 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 trajectory. A light-year represents the distance light travels in a year, equivalent to 9.5 trillion kilometers.
These stars became part of the Milky Way following a galactic merger that occurred approximately two billion years after the Big Bang. The dwarf galaxy where they originated was named Low-energy-Kraken-Heracles (LKH) based on previous studies exploring the possibility of such a primordial merger.
Lead author Davide Massari, an astrophysicist at the National Institute for Astrophysics in Bologna, Italy, highlighted the key discovery of the galaxy’s first merger event in its early stages.
The study sheds light on the debate surrounding the Milky Way’s early growth, indicating that the merger introduced a significant influx of stars and interstellar gas, fueling star formation and contributing to the presence of dark matter within the galaxy.
Massari described the merger as “peaceful” in terms of star interactions but more “explosive” in terms of gas dynamics, suggesting that the collision between gases from LKH and the Milky Way likely triggered the formation of numerous stars.
The Milky Way has been involved in two other major galactic mergers, absorbing the Gaia-Sausage-Enceladus dwarf galaxy about 1.8 billion years post the LKH merger and subsequently 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 Earth, underscoring the importance of understanding the Milky Way’s historical evolution in addressing fundamental questions about our origins.
