Actually it was both :)
If anyone here is interested in a good read explaining the physics and offering an explaination for the Great Attractor, Stephen Baxtor has a series of novels about this phenomenon: “Ring”, “Flux”, and “Vacuum Diagrams”. or “ Xeelee: An Omnibus: Raft, Timelike Infinity, Flux, Ring by Stephen Baxter (2010)” “Vacuum Diagrams” offers more detail.
Maybe the vacuum of space , and the density of that vacuum, is not constant.