May 18, 2014
Nebulas can be created several ways in After Effects: with "cards in space" of real images, or generated by Fractal Noise or 3D particle systems, commonly fractal-displaced particle arrays like Trapcode Mir, Form, or perhaps Hiltfilm Atomic Particle and others.
Nebula construction in After Effects collects a few resources, most notably Nebula Construction Kit, a video guide to a free AE project file using Trapcode Mir from Peder Norrby of Trapcode.
See the rest at PVC... and for the meantime, here's background from the Hubble Space Telescope:
by Rich at 11:16 AM