Hey! Wait a minute and check out also my newest space art tutorial! [link] You can create with this tutorial not only nebulae, but WHOLE SPACE ART SCENE! 
Enjoy! Nebula tutorialSpecial thanks goes to UnrealPL for motivating me to do this tutorial.Pack includes tutorial in jpeg, 700x10000px (quite big
) and two stock photos, which I've used to make this nebula. Nebula was made special for this tutorial.
Hope it will be helpful. Every comments, advices and suggestions appreciated. And every fav+ too
Edit:
Now I have new monitor, so I see some areas in final outcome, which are not correctly erased. You can see these artifacts in the left side and in the right corner of image. But why we need to be so scrupulous? ;D enjoy your creativity
bye
`ChewedKandi has certainly gone out of her way to keep the vector community on the right path. Always making sure that her talents are infinitely scalable, Sharon has put her bezier curves to excellent use, and firmly anchored herself as an inspirational leader. We're absolutely delighted to bestow the Deviousness Award for June 2013 to `ChewedKandi. Congratulations, Sharon! Read More
Sta.sh
i think you should add fractals like i did and dodge and burn tools