Artistic rendering of Enceladus being devoured by a Milky Way-like galaxy. Image: René van der Woude,
Milky Way merged with a large galaxy ten billion years ago - space short science news

Some ten billion years ago, the still young Milky Way merged with another large galaxy that astronomers have baptized Gaia-Encladus. The stars of Gaia-Encladus make up most the Milky Way’s halo and also shaped its thick disk, giving it its inflated form. The data used for this study were provided by the second mission of the Gaia satellite, giving information about 1.7 billion stars. The researchers found that the chemical signature of many halo stars was clearly different from original Milky Way stars, and that both formed a rather homogenous group. Thus, the Milky Way was formed by the fusion of two galaxies, rather than by fusion of many small ones.

Read the full story: University of Groningen
Scientific publication: Nature