Download Lightroom presets and LUTs, absolutely free. Use the presets to add creativity and style to your photos.
Make sure you select a created layer and set Default Background and Foreground colors (D or Icon next to the switching colors). Go to Filter > Render > Clouds... In your ellipse should appear clouds. Add another filter - Difference Clouds (Filter > Render > Difference Clouds...). You should get similar like in image below.
To better understand the structure of the future nebula, change the Blending mode for this layer to "Color Dodge". Repeat apply filter "Difference Clouds", using Cmd/Ctrl+ F or Filter > Difference Clouds. Keep hitting Cmd/Ctrl+ F until you get the desired result or at least 9000 times :).