Jt

A planetary nebula is the photogenic successor to the red-giant stage of stellar evolution, through which relatively lightweight stars those with about one to eight solar masses eventually pass. Red giants slough off voluminous quantities of dust grains, providing future star factories with essential shielding and catalysis. it is fair to assume that we know exactly what materials need to be recycled, how much of them will be produced, and at what time. This is akin to...

Processing and production

Now let us look in some more detail at what winds up in the ISM, how it gets there, and where it is headed. The ISM is a vast collection of gas and dust between the stars. The gas is primarily hydrogen, in atomic form (H) in warm regions, and in molecular form (H2) in cold regions (those with temperatures below about 100 Kelvin). The dust is really more like smoke in that the individual grains are very small compared to terrestrial dust particles, but each contains too many atoms to be...

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'...

Rattling the conveyor belt Herbig Haro objects like this lightyearlong object are the visible manifes

These flows have now been shown to extend for tens of light-years out into the ISM, even though they originate in circumstellar regions only about the size of our solar system. The flows are very long and narrow, so the naive orange-juice drinker would think that they cannot affect a very large volume of the ISM. Actually, though, the frozen-concentrate buyer would realize that the flows can indeed influence very large volumes. How so We said earlier that molecular cloud cores...