I smell render failure. 🙂
Seriously, you might want to fake it with a NASA galaxy shot. Mask it around the stars and feather the mask. Dupe the layer, make the dupes 3D layers, and separate them all a bit in Z-space. Leave the middle layer’s mask alone, but shrink (negative expand) the mask on each of the layers on either side of it, so the mask gets smaller as you go out.
It’s like making a sphere using circle planes: the middle one is biggest, with the others getting progressively smaller as you go out.
This way you can fly into a galaxy and pass through layers of stars. Add a few stars in-between and near camera path for effect.
Give it a go …