Just as each soul spark of every living cell in our bodies makes up that which we call our soul, so too do all living souls in the world cumulatively make up part of a universal soul. Indeed, mysticism teaches us that the soul giving us vitality is connected to, and draws sustenance from, a universal soul.
Perhaps they are not stars, but rather openings in heaven where the love of our lost ones pours through and shines down upon us to let us know they are happy.