Milky Way Swallowed Dwarf Galaxy 11.8 Billion Years Ago

Our Milky Way galaxy has a complex history of growth, with new research revealing a significant milestone: a merger with a dwarf galaxy about 11.8 billion years ago. This ancient event occurred when the universe was less than 15% of its current age. The discovery sheds light on how the Milky Way achieved its current dimensions, not only through internal star formation but also by absorbing smaller galaxies.

The dwarf galaxy, named LKH, had a stellar mass equivalent to 500 million suns at the time of the merger. Scientists used data from the Hubble and Gaia telescopes to analyze stellar clusters, determining their age, chemical composition, and trajectories. This merger infused the Milky Way with a substantial amount of stars and interstellar gas, fueling further star formation and contributing dark matter.

While the merger was relatively peaceful for stars, the interaction of gas from both galaxies likely triggered a burst of star formation. The Milky Way has undergone other mergers, including with Gaia-Sausage-Enceladus and the ongoing absorption of the Sagittarius dwarf galaxy. These past events have collectively influenced the formation of our solar system and Earth, offering insights into our cosmic origins.