Milky Way's Earliest Known Galactic Merger with a Dwarf Galaxy Revealed

Astronomers have discovered the earliest known merger of the Milky Way, which occurred approximately 11.8 billion years ago, at a time when the universe was less than 15 percent of its current age. The dwarf galaxy involved had a mass equivalent to 500 million suns, roughly a quarter of the Milky Way's mass during that period. A team led by Davide Massari from the National Institute for Astrophysics (INAF) in Bologna, Italy, examined stellar clusters within the Milky Way's central 20,000 light-years, utilizing data from Hubble and Gaia. They identified that these stars came from a galaxy called Low-energy-Kraken-Heracles (LKH), which merged with the Milky Way around 2 billion years post-Big Bang, enriching it with interstellar gas and dark matter that stimulated star formation.