I don't mean when stars in a binary system spiral in and fuse together. I mean when they undergo a fast head on collision in an elliptical galaxy. I assume it's much rarer for stars to undergo that type of collision in a spiral galaxy than in an elliptical galaxy because in a spiral galaxy, every star is pretty much moving at velocity that depends on its position in the galaxy. Has anyone observed a collision of that sort? Do the stars explode into a ring nebula, that is a nebula that's expanding too fast for its gravitational attraction to itself to pull it into a crab nebula, because they collide at such a high speed that gravitational attraction is not enough to make them combine into a larger star?