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Tom Mazanec
2012-Jul-23, 12:29 PM
How much energy does a gram falling into a Black Hole release?
How would this compare to turning the gram into energy completely?

Hornblower
2012-Jul-23, 12:55 PM
How much energy does a gram falling into a Black Hole release?
How would this compare to turning the gram into energy completely?When a body falls into a black hole, if I am not mistaken, general relativity predicts that a portion of the total energy of the combination will be emitted in the form of gravitational wave radiation. I do not have the knowledge to calculate how much that would be. I would expect it to be far less than the energy equivalent of a whole gram. After all, when surrounding stuff falls into a black hole, the mass of the black hole increases.

ShinAce
2012-Jul-23, 02:51 PM
How much energy does a gram falling into a Black Hole release?
How would this compare to turning the gram into energy completely?

I don't think that's a straight forward question.

Are we talking about a gram falling into a starving black hole? Is it a gram of the accretion disk you're asking about? Or even a gram positioned very carefully within the ergosphere of two in-spiralling black holes?

The first gives you practically no energy. The second a bit of energy. The third a bit more.

Grey
2012-Jul-23, 03:23 PM
This got me thinking. The total waste collected annually in the world is about 109 tons (from here (http://unstats.un.org/unsd/environment/wastetreatment.htm)). The total energy used annually is close to the energy equivalent of about 10 tons of matter (from here (http://en.wikipedia.org/wiki/Orders_of_magnitude_%28energy%29)). If you could get an extraction process that's at least a millionth of a percent efficient (probably by the second method ShinAce suggested, sending matter on a trajectory into the accretion disk and then capturing some of the resulting radiation), you could provide power to everyone on the planet and simultaneously get rid of all their garbage. Of course, you'd need to have a convenient black hole lying around. Oh, and you'd want to make sure you didn't throw something away if there were a chance you might want it again later. ;)

ShinAce
2012-Jul-23, 03:49 PM
What about the obvious problem. How much energy does it take to launch a billion tons of garbage into space(without a space elevator)? Won't that simply create more waste?

Living in Canada, we see a fair share of recycling. Beer cans and bottles have a nearly 99% return rate. We typically sort household recyclables into: paper, tin, glass, and plastics. It wasn't until I was in Richmond, Virginia that I saw my sister throw everything into a garbage bag. Richmond did not have recycling. I was shocked. But then I realize that even hazardous waste depots are a pain. Why don't we have a semi-annual household waste pick-up? That might motivate people to stop throwing batteries and such into the garbage.

I don't see it as a garbage problem. I see it as a recycling problem. It's cheaper to throw it out, so out it goes.

At any rate, the third way to extract energy is called the Penrose process: http://en.wikipedia.org/wiki/Penrose_process
It works by means of using the black hole's angular momentum. Kind of like a gravity assist, or slingshot maneuver.

Grey
2012-Jul-23, 04:57 PM
What about the obvious problem. How much energy does it take to launch a billion tons of garbage into space(without a space elevator)? Won't that simply create more waste?That's just an engineering detail. ;) But actually, although the energy to launch into space is pretty large for most purposes, compared to the rest energy of the mass launched, it's actually pretty small. A rough calculation for the Saturn V is about 1016 joules to lift 30,000 kg to the moon. That's a huge amount of energy, but it's only the equivalent of about 100 grams of mass. I was pretty much just counting that as one of the net losses in the system, along with conversion from the intense radiation of an accretion disk into usable energy, and transmission back to Earth. It's significant, but not enormously so. It's the reason nuclear power uses so little fuel, and fusion is so captivating: if you can manage to convert even a small fraction of some bit of matter into energy, you can have huge losses along the way and still come out ahead. I obviously wasn't entirely serious when suggesting this (at least I hope it was obvious), but as far as physical feasibility, it really could be done.

Living in Canada, we see a fair share of recycling. Beer cans and bottles have a nearly 99% return rate. We typically sort household recyclables into: paper, tin, glass, and plastics. It wasn't until I was in Richmond, Virginia that I saw my sister throw everything into a garbage bag. Richmond did not have recycling. I was shocked. But then I realize that even hazardous waste depots are a pain. Why don't we have a semi-annual household waste pick-up? That might motivate people to stop throwing batteries and such into the garbage.

I don't see it as a garbage problem. I see it as a recycling problem. It's cheaper to throw it out, so out it goes.Yep. Since we don't have a convenient black hole handy (and since the "engineering details" that I've swept under the rug might be beyond our current technological capability at the moment even if we did!), recycling is a much better option.

publiusr
2012-Jul-28, 07:01 PM
The removal of energy should destroy a black hole. I wonder what else it could be used for: