Layout your pieces as shown and start creating a
sandwich with the base layer being the star field
followed by the Base Grid and the bulge/vortex. If
you want the planet to appear as if it is inside the
bulge just place it between the grid and the bulge
layer.
You may want to add a black circle, the same
diameter as your Bulge behind the Bulge it self as
long as it isn’t important that the star field show
through the grid. This means creating another
sandwich with the black disk at the back, the planet
in the middle and the grid on the top. It will save you
having to render the bulge grid one more time once
it is in position on the base grid.
 
Add stars as required but remember to vary the size
of them. I would usually make 2 or three different
stars so they don’t all look like clones of each other.
The stars are nothing more than a white circle that
has been blurred and, if necessary, had some trans-
parency applied, with a Shape star on top of it.
 
Since the heavens are not uniformly populated with
an even number of stars, you may want to dim some
and render others invisible, especially if you’re trying
to create a black hole kind of effect. it’s simple
enough to draw a shape(s) just above the back-
ground layer, blur it, and add either directional or
a general transparency.