A recent study sheds light on the journey of the Milky Way galaxy, home to billions of stars, including our sun. Researchers have uncovered evidence of a significant event in the galaxy’s history, revealing that the Milky Way absorbed a smaller galaxy approximately 11.8 billion years ago when the universe was young.

This galactic merger, the earliest known for the Milky Way, highlights how the galaxy evolved not only through internal star formation but also by merging with smaller galaxies within its gravitational reach. The smaller galaxy, classified as a dwarf galaxy, contained stars with a mass equivalent to 500 million suns at the time of the merger, about a quarter of the Milky Way’s size then.

By studying stellar clusters near the Milky Way’s center using the Hubble and Gaia telescopes, researchers analyzed the age, chemical composition, and trajectory of the stars. These stars, part of the Milky Way after the merger, originated from a dwarf galaxy named Low-energy-Kraken-Heracles (LKH), involved in the galaxy’s early growth around two billion years after the Big Bang.

Astrophysicist Davide Massari, lead author of the study published in Nature Astronomy, emphasized the significance of this discovery, calling it the first merger event experienced by the Milky Way in its infancy. The study suggests that the merger infused the Milky Way with stars, interstellar gas, and dark matter, fueling star formation.

While the merger was peaceful for stars, it was more explosive for gas, likely triggering the formation of numerous stars. The Milky Way has been part of other significant mergers, including with the Gaia-Sausage-Enceladus and Sagittarius dwarf galaxies, all influencing the formation of the solar system and Earth. Understanding the Milky Way’s past helps answer fundamental questions about our origins.