I'm still not satisfied with the difficulty curve myself and I'm planning to add 24 levels after the voting period to assess it.
I only put 8 levels in the game jam version because I know that everyone has a lot of playing to do and I didn't want to steal too much time :-)
But I have ideas about new levels with dual black holes and new shooting mechanics (dual shooting, propelling) to spice it up and add some more problem solving depth.