All good suggestions, so far. Here's another idea. SID around stars, treat the large white areas as 4 squares...quilt a 1/2 cross-hatch in each square (alternating directions). The finished look will be concentric squares "on point" within that space. You could embellish further by quilting a design of your choice within the alternate spaces between the lines. For the smaller white squares which exits at the junction of two stars, perhaps a greek key? I can't imagine how difficult free-hand work would be on a domestic machine...straight lines seem to be an easier option with that equipment. Good luck!