Sagittarius Tidal Stream

The Sagittarius Stream is a long, complex, structure made of stars that wrap around the Milky Way galaxy in an almost polar orbit. It consists of tidally stripped stars from the Sagittarius Dwarf Elliptical Galaxy resulting from the process of merging with the Milky Way over a period of billions of years.

Association with spiral arm layering

The shredding apart of a large intruding collection of stars in the indefinite past appears to have sent oscillations analogous to sound waves through the Milky Way spiral arm structure. The effects of the oscillations are observed today as vertically stacked layers of alternately denser and sparser star distributions. Presently, the Sagittarius Stream is positioned relative to the observed layers such that its progenitor, the Sagittarius Dwarf Elliptical Galaxy, is the strongest candidate intruder whose wake left behind the disturbance in the spiral arms.