Tutorial by: Peder Norrby
Peder is a genius in all things trapcode, as seen by his amazing work here, but he has given us all a glimpse into his awesomeness by providing source files for us to create this amazing galaxy / nebula particular effect!
From the instructor:
Create nebulae in After Effects with Trapcode Mir and Form.
Tutorial on using the Nebula Construction Kit AEP.