How can Nebulae be harvested?
My question is about a far off and seclusive colony in the reaches of the Orion nebula. As they are relatively isolated they have resorted to harvesting the nebula itself for resources.
What I want to know is how this can accomplished and what would be needed to facilitate it?
This can include futuristic technology as long as it is conceivably possible.
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1 answer
It's incredibly impractical to attempt to harvest a nebula.
Density of a Nebula is somewhere between 100 and 10,000 particles per cubic centimeter. Really, really young nebula can have about 1,000,000 particles per cubic centimeter.
For comparison, sea level atmosphere has about 25,000,000,000,000,000,000 particles per cubic centimeter. The theoretical maximum vacuum you can create at sea level is aproxamately 0.0008534% of an atmosphere - Or a density of roughly 213,350,000,000,000 particles per cubic centimeter.
To put it simply, the theoretical "Best" vacuum you can achieve on Earth is about 213 million times more dense than the densest of nebula.
Fun Fact: The atmosphere on the Lunar Surface is between 80,000 atoms per cubic centimeter and 1,000,000 atoms per cubic centimeter, depending on which part of that article you look at. That's roughly about the same density as a nebula.
Now, let's do some more math.
Helium has a density of 0.0001785 grams per cubic centimeter. Not a lot. It has an Atomic Mass of 4.002602. This means one Mole of Helium is a tad over 4 grams. Using this, we can get that one cubic centimeter of Helium at one atmosphere is around the ballpark of 26,856,000,000,000,000,000 individual particles, or atoms, of Helium.
In the thickest nebula, you would have to collect 26,856,000,000,000 cubic centimeters. That's just shy of 27 cubic kilometers of "space" to get one cubic centimeter of Helium.
(A note: I was thinking of Helium-3 when writing this, as it's used in a lot of sci-fi space reactors. But it turns out Helium-3 has an atomic mass of 3.0160293 and not 4.002602. I'll probably go back and re-do the math in the morning, unless someone answers better than I.
Also, it's fairly late for me so my math exacts may not be 100% correct. The general idea should be fairly correct even if the numbers aren't.)
For nearly anything I can think of, the energy you would get from harvesting that material would not equal the energy expenditure that you would have to make to harvest it.
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