The Gaia-Enceladus collision
The Milky Way swallows a galaxy a quarter its size, and still wears the debris.
- When
- Known to
- ± 500 million years
- Era
- Enrichment, Stelliferous
Around ten billion years ago a dwarf galaxy now called Gaia-Enceladus, or the Gaia Sausage, fell into the young Milky Way. Gaia's measurements of stellar motions revealed its remains as a vast population of stars on strongly radial orbits — most of the inner halo. The impact heated the existing disk into the thick disk we see today, and it is the last major merger our galaxy experienced.