With the same paint program and based on the same image, create
a greyscale image to use as the alpha channel. I found it
easiest to think about making the parts I wanted to glow white
and the parts that should stay dim black, but as it turns out
I had to invert the alpha when I imported it.
Create a sphere. Go into the Material Lab. Start with the
default material. Click in the A column for Diffuse, Ambient,
Transparent (color) and Transparency. Leave the Transparency
slider set to zero. Tell the A component that its source is
Go into the Texture Source Editor and load the color version
in the first box and the alpha channel in the second box.
You'll know if you have to invert the alpha channel
if the result in the third box is mostly transparent.