HUBBLE TELESCOPE FINDS EVIDENCE OF MILKY WAY'S EARLIEST GALACTIC MERGER

New observations from NASA's Hubble Space Telescope have provided definitive evidence that the Milky Way consumed a dwarf galaxy roughly 11.8 billion years ago, according to research published in Nature Astronomy. The merger occurred approximately 2 billion years after the Big Bang, making it the earliest known galactic collision involving our galaxy. Scientists examined star clusters gathered near the Milky Way's centre using data from the Hubble and Gaia telescopes, analysing their age, chemical signature and trajectory. The absorbed dwarf galaxy, named Low-energy-Kraken-Heracles (LKH), is estimated to have contained stars with a combined mass 500 million times that of the Sun at the point of collision.

The discovery extends knowledge of the Milky Way's history 1.8 billion years farther back than previously established. Astrophysicist Davide Massari of the Astrophysics and Space Science Observatory of Bologna in Italy, lead author of the study, stated that the finding represents "the unambiguous discovery of the first merger event experienced by our galaxy in its infancy." Researchers examined stellar clusters within the galaxy's innermost 20,000 light-years, each comprising hundreds of thousands of stars. The Milky Way has undergone other documented mergers, including with the Gaia-Sausage-Enceladus dwarf galaxy 10 billion years ago and an ongoing merger with the Sagittarius dwarf galaxy that began over 6 billion years ago.

Whether the Milky Way's early growth was driven by internally generated star formation or by galactic mergers has been a matter of scientific debate. The new evidence demonstrates that the galaxy expanded not only by creating its own stars but by absorbing smaller systems drawn into its gravitational influence. Observations and simulations had previously suggested that an ancient merger preceded the documented Gaia-Sausage-Enceladus event, though specifics remained contested. The research resolves this longstanding question about the galaxy's formative history.