The reason I'm asking is that I've seen a lot of images lately of nebulae with newly forming stars, particulary from Spitzer, that show a large blue star (or small group of big stars) that is central to a bubble of gas, with new smaller stars forming in areas of compressed gas. The typical explanation seems to be that the central big star is blowing out the gas bubble with its stellar wind. Thus its seems that the big star promotes the formation of the smaller stars. So, you should typically see clusters with a few big stars in the middle and smaller stars surrounding. Any comments?