The Bar of stars and the Spiral Arms in Galaxy Evolution.

The Bar of Stars and connection to the Spiral Arms.

The Bar of stars and the Spiral Arms may be part of the same structure that spans the whole galaxy. If that spiral is unwound, to line up with the Bar, it will form one continuous double jet like structure from the Central Object to the outer Halo(below).
This jet is a straight line across the Bulge as it is trapped in a strong magnetic field and becomes a spiral once evacuated from this due to gradual slowing in spiraling action.
That process may be part of the connection between galaxy evolution and the Central Object as the Bar, in this scenario, is formed by matter blasting off it's surface in two opposite directions.
The Spiral Arms are the Bar of yesteryear in a recognition of outward drift and rotation, from the Central Object, that forges the entire galaxy in growth. Any merger would result in the deformation of the spiral which conflicts with the Standard model.