full cycle
In general, humans build great edifices and nature eventually destroys them. We humans should take solace, then, in the fact that nature sees fit to destroy not just our great works but its own as well. The great recycling plants that are molecular clouds are ultimately limited, and then destroyed, by their own success. Supernovae and other powerful stellar winds push material around, and the en-
ergetic photons from hot young stars eat away at gas that could have extended those stars' families. The famous Hubble Space Telescope images of the Eagle Nebula and NGC 3603 show pillars of dense gas enduring obvious erosion. Before a giant molecular cloud gets a chance to consume all its gas, its progeny will ruin its chances for survival.
Hubble's image of NGC 3603, shown below, presents us with a beautiful composite of the entire interstellar recycling process. At the center of the image we see the consumption phase in action, with young stars burning bright. To the upper left of the cluster we see a ringed, dying
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