Milky Way consumed galaxy LKH 11.8B years ago: Hubble finds

Using data from the Hubble Space Telescope, astronomers have found definitive evidence that the Milky Way galaxy consumed a dwarf galaxy named LowenergyKrakenHeracles, or LKH, approximately 11.8 billion years ago. This ancient merger, occurring just two billion years after the Big Bang, now stands as the earliest known major collision in our galaxy's history, significantly extending the timeline of the Milky Way's growth by nearly 2 billion years.

The discovery was made by a team led by Davide Massari of the Astrophysics and Space Science Observatory of Bologna in Italy. By studying the age and chemical composition of 39 globular clusters in the inner region of the Milky Way, researchers identified a third distinct population of stars. These clusters were older than those captured during the previously known merger with the Gaia-Sausage-Enceladus galaxy about 10 billion years ago, but younger than the Milky Way's most ancient native clusters. This indicated an earlier, separate accretion event.

"Thanks to the high resolution and depth of Hubble imaging, we could measure the age and the metal content of these clusters with unprecedented precision," said study co-author Chiara...