In the renderer. If you're using POV, it's a pattern modifier command.
You've actually got 90% the right idea--a sphere with a gradient in it--you just need to swirl it around a bit.
I hadn't done my blog post for the day yet and I needed a topic, so I coded up an example:
http://www.independentdeveloper.com/...sma-in-pov-ray
Believe-it-or-not, it's almost exactly the same thing you've got cooking in your scene, it's just applied as turbulent media. What's nifty is that if you do it in POV, it's an actual 3D thing... you can rotate around it, do animations, etc. On my post, I rendered a turntable of the plasma so you can see what I mean.
Oh! You might also have fun with this site. It's macros for making nebula in POV:
http://www.geocities.com/SiliconVall...34/galaxy.html