Big stars tend to stick together.  They all require incredibly dense regions in which to form, but once they do, they do a great job of blowing away and ionizing any other gas and dust in the vicinity.  This is why nebulas in distant galaxies are great tracers of massive star formation.  The bigger and hotter the star, the more UV light it produces, the more it ionized a gas cloud, the more we see gorgeous nebula.  So it’s no surprise that when I look at the nebula below, I can guess that the central stars are huge, outweighing our...