Another problem with all this discussion about what the phenomena at the end of Empire is, is that we're evaluating it based on astronomical photography, which isn't really that reliable as it is rarely standard optical photography. However, that is the common conception of what interstellar phenomena look like, and perhaps the wisest choice artistically.

One of the physicists talking about it over on theforce.net says it can't be a galaxy because galaxies don't really look like that to the naked eye, which is what we're seeing in that scene. But he completely overlooks the fact that 99.9% of people sitting in a movie theatre won't have any idea that a spiral galaxy is substantially dimmer and actually pretty hard to see with the naked eye. Most of us think they're bright white (sometimes yellowish) with spiral arms around a bright bulbous centre, but that's not true.

Not that any of this matters a jot, as long as the image looks good on screen while not negatively impacting on the narrative.