I made the ring galaxy as a multi-layers object that can be toggled with a CELX script. This way, we can have several rendering of the same galaxy.
Here's the default representation, using a 256 X 256
custom PNG template (default rendering style in Celestia) :
RingUniverse.png
Unfortunately, this template needs to be placed in the base
models folder, and isn't recognised by Celestia if it's placed in the
extras folder.
Here's a preview of the default rendering in Celestia. The arms fits perfectly well with the stars distribution :
default.jpg
Here's the default template superposed with a part of the sprites model (the other part isn't shown here since we can't show more than three pictures in a message, and I'm too lazy to use my personnal server space

) :
superposed.jpg
I didn't made the central core yet.