How would you stabilize that? I feel like there would have to be a constant connection to that dimension and the gravity it's storing as well as some force keeping it there. Plus would we really trust a giant orb that visits us by storing its gravity else where while all of a sudden we get invaded by a great darkness? Could it be the darkness is just pissed the traveller keeps putting all it's gravity in his house throwing off it's feng shui? I'd also be upset if I'm some sort of deity and all of a sudden my house just crumples because some dick decided it was totally cool to store his massive gravitational pull in my dimension and more specifically on top of my home crushing everything except for my immortal self. Now I'm homeless and upset and set my army forth to ruin everything he cares for which just so happens to be the solar systems he visits and helps improves their lives this time around being us. We're just unfortunate collateral damage from the revenge of the darkness.