What ancient merger remnant in the Milky Way is also called the Gaia Sausage?

Gaia-Enceladus is the ancient Milky Way merger remnant also called the Gaia Sausage.

It is the debris of a dwarf galaxy that collided with and was absorbed by the young Milky Way roughly 8–11 billion years ago. Gaia’s measurements showed that many halo stars share unusual motions: they travel on elongated, highly radial orbits rather than following the nearly circular paths typical of the Galactic disk. When those orbital patterns are plotted, the distribution resembles a sausage, giving the structure its informal name.

The merger was identified through the combination of stellar motions, chemistry and ages. Its debris now forms a major component of the Milky Way’s inner stellar halo and likely contributed to the Galaxy’s thick disk. Several globular clusters are also associated with the accretion event.

The names Gaia-Enceladus, Gaia Sausage and Gaia-Sausage-Enceladus refer to the same broad merger remnant, although studies can differ in how they divide its stellar populations. Sagittarius Dwarf is a separate satellite currently being disrupted, while the Magellanic Stream is a gas trail linked mainly to the Magellanic Clouds.