Milky Way absorbed a massive galaxy 11.8 billion years ago

Astronomers have discovered evidence of a massive galactic merger that occurred approximately 11.8 billion years ago, significantly earlier than previously understood. This event involved the Milky Way absorbing a dwarf galaxy identified as Low-energy-Kraken-Heracles (LKH).

This discovery, published in Nature Astronomy and led by Davide Massari, pushes back the timeline of the Milky Way’s major collisions by about 1.8 billion years. Previously, the Gaia-Sausage-Enceladus merger, which occurred roughly 10.5 billion years ago, was considered the primary early formative event.

Researchers utilized data from the Hubble Space Telescope and the European Space Agency’s Gaia mission to analyze 39 globular clusters within the Milky Way’s inner 20,000 light-years. By examining the chemical composition, age, and movement of these star clusters, the team identified a distinct population of stars that originated from the LKH galaxy. This merger helped shape the proto-Milky Way during a period when the universe was less than 2 billion years old.