Our Milky Way Galaxy’s Most Recent Major Collision
Artist’s conception of the Milky Way galaxy. Credit: Pablo Carlos Budassi
One of the characteristic features of modern cosmology is its description of how galaxies evolve: via a hierarchical process of colliding and merging with other systems. Nowhere in the universe do we have a clearer view of this buildup than in our own 
A photograph of the Small Magellanic Cloud, a nearby dwarf galaxy that is merging with the Milky Way. (The foreground globular cluster 47 Tucana is seen at the right.) Astronomers using the Gaia mission and the new H3 Survey of stars in the Milky Way’s halo have shown that the Galaxy’s last major merger was with a dwarf system known as Gaia-Sausage-Enceladus about 8-10 billion years ago, and about half of the stars in the galactic halo descend from that system. Credit: Jose Mtanous
The Gaia spacecraft was launched in 2013 with the goal of making a precise three-dimensional map of the Milky Way by surveying 1% of its approximately 100 billion stars. DOI: 10.3847/1538-4357/ac2d2d
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