New research has shed light on the complex journey of the Milky Way galaxy, home to countless stars including our sun. Scientists studying star clusters near the Milky Way’s core have uncovered evidence of a significant event from 11.8 billion years ago when a smaller galaxy was absorbed by our galaxy. This marks the earliest galactic merger for the Milky Way, showcasing its growth not only through internal star formation but also through the assimilation of smaller galaxies.
The smaller galaxy involved in the merger was classified as a dwarf galaxy, containing stars equivalent to 500 million solar masses at the time of the merger, representing a quarter of the Milky Way’s size then. By analyzing stellar clusters within the Milky Way’s innermost 20,000 light-years using the Hubble and Gaia telescopes, researchers determined the age, chemical composition, and trajectory of these stars.
The merger event, occurring about two billion years after the Big Bang, integrated stars from a dwarf galaxy named Low-energy-Kraken-Heracles (LKH) into the Milky Way. This discovery, detailed in a study published in Nature Astronomy by lead author Davide Massari, highlights the first known merger experienced by our galaxy during its early stages.
The study suggests that the merger injected a substantial amount of stars, interstellar gas, and dark matter into the Milky Way, fueling star formation. While the merger was relatively peaceful for stars, the collision of gases likely triggered significant star formation. The Milky Way has been involved in two other major mergers, including one with the Gaia-Sausage-Enceladus dwarf galaxy and ongoing interaction with the Sagittarius dwarf galaxy.
Massari emphasized that reconstructing the Milky Way’s history contributes to understanding our origins and the formation of our solar system. The implications of these galactic mergers extend to shaping the events that led to Earth’s existence.