Referencing an instantiated object with a global variable

I'm instantiating an object and plan to destroy it in another function, so i'm trying to reference it through a global variable. I'm currently doing

void DrawScore() {

     GameObject a;
     GameObject b;
     GameObject c;

     Vector3 star1Pos = GUIdrawCentre - new Vector3(+GUIdrawOffset,0,0);
     Vector3 star2Pos = GUIdrawCentre;
     Vector3 star3Pos = GUIdrawCentre - new Vector3(-GUIdrawOffset,0,0);

     if(starCount == 0)
     {

     }

     if(starCount == 1)
     {
         a = Instantiate(GUIstar, star1Pos, Quaternion.identity) as GameObject;

         _stars[0] = a;
     }

}

then in another scripts, looping through the array and destroying each member.

_stars[] is an array of GameObjects declared globally

For whatever reason, _stars[0] is always set to "none" and never gets overwritten with anyt$$anonymous$$ng.

Any ideas why t$$anonymous$$s is happening? I've used the same method in other projects but t$$anonymous$$s time it just isn't working