Gaia Sausage

The Gaia Sausage or Gaia Enceladus is the remains of a dwarf galaxy (known as the Gaia-Enceladus galaxy, Sausage Galaxy, Gaia-Enceladus-Sausage, or Gaia-Sausage-Enceladus) that merged with the Milky Way about 8–11 billion years ago. At least eight globular clusters were added to the Milky Way along with 50 billion solar masses of stars, gas and dark matter. It represents the last major merger of the Milky Way.

Etymology

The "Gaia Sausage" is so-called because of the characteristic sausage shape of the population in a chart of velocity space, in particular a plot of radial (

v

r

{\displaystyle {\boldsymbol {v}}_{r}}

) versus azimuthal velocity (

v

θ

{\displaystyle {\boldsymbol {v}}_{\theta }}

) of stars (see Spherical coordinate system), using data from the Gaia Mission. The stars that have merged with the Milky Way have orbits that are highly elongated. The outermost points of their orbits are around 20 kiloparsecs from the Galactic Center at what is called the "halo break". These stars had previously been seen in Hipparcos data and identified as originаting from an accreted galaxy.

The name "Enceladus" refers to the mythological giant Enceladus, who was buried under Mount Etna and caused earthquakes. Similarly, this former galaxy was buried in the Milky Way, and caused the puffing up of the thick disc.

Components

Globular clusters

The globular clusters firmly identified as former Sausage members are Messier 2, Messier 56, Messier 75, Messier 79, NGC 1851, NGC 2298, and NGC 5286.