Ancient Galactic Collision Revealed: Milky Way Merged with 'Low-energy-Kraken-Heracles' 12 Billion Years Ago

A new analysis of globular-cluster ages has uncovered evidence that the Milky Way swallowed a sizeable galaxy, now called Low-energy-Kraken-Heracles, roughly 12 billion years after the Big Bang. Lead author Davide Massari and colleagues employed precise age measurements from Hubble Space Telescope observations, revealing three distinct cluster age groups: native Milky Way stars, those from the previously known Gaia-Sausage-Enceladus event, and an intermediate set linked to the newly identified satellite.

The research, appearing in Nature Astronomy, confirms a long-debated third major merger and aligns with earlier suggestions by astronomers such as Duncan Forbes. Luca Casagrande noted that while the Milky Way’s growth through multiple collisions is expected, detecting older mergers remains challenging. The study underscores that the galaxy continues to evolve, currently interacting with the Sagittarius Dwarf and potentially facing a future encounter with Andromeda. Researchers caution that additional, yet-undiscovered mergers may still be revealed as more data become available.