The care and feeding of black holes

[Junghalli]

I've been designing a ship that's supposed to have an artificial singularity for a power source (yes, this is somewhat vaguely to the other topic I posted, but only tangenitally).
Anyway, I entered in the value for a two million ton artificial singularity in the Xaonon Hawking radiation calculator (http://xaonon.dyndns.org/hawking/) and it gave an energy output of somewhat less than 10 TW, which is around what I had in mind (taking into account inefficiencies of course).
So, if you put a two million ton mass singularity into a tub of, say, compressed gas would it start to pull in matter of its own self-gravity? Or would you have to find some more artificial way of feeding it, like holding it on the crossbeams of two continuously firing particle accelerators?

[Surlethe]

So, if you put a two million ton mass singularity into a tub of, say, compressed gas would it start to pull in matter of its own self-gravity?

It depends on the size of the tub. If it's a really, really small tub, then yes. Otherwise, it would take a while for it to pull the gas in as a matter of gravity (though I wonder what role the gas' pressure would play on it? That sounds like an interesting chemistry problem).

Or would you have to find some more artificial way of feeding it, like holding it on the crossbeams of two continuously firing particle accelerators?

This would be more efficient, I think.

When you make a singularity reactor, you also have to find a way to keep it attached to your ship. Since you can't literally attach it to anything, the moment you accelerate, it's literally going to fall back through your ship, since it's so dense and so small (a radius of millimeters, I guess).

[Junghalli]

It depends on the size of the tub. If it's a really, really small tub, then yes. Otherwise, it would take a while for it to pull the gas in as a matter of gravity (though I wonder what role the gas' pressure would play on it? That sounds like an interesting chemistry problem).

So basically you want a very, very small "feeding chamber" into which gas is continuously forced at high pressure?
I figured on using a high pressure gas because that way more molecules were likely to wander close enough to it to be sucked in.

This would be more efficient, I think.

I had in mind having it self-accreate, if possible, because that way you could use just about anything for fuel. Possibly even feed the ship's sewage line into it or something, anything with matter would do.

When you make a singularity reactor, you also have to find a way to keep it attached to your ship. Since you can't literally attach it to anything, the moment you accelerate, it's literally going to fall back through your ship, since it's so dense and so small (a radius of millimeters, I guess).

When I was discussing it on another message board one of the guys there said a singularity could actually be given a positive or negative charge. So I'm thinking of holding it in place magnetically.

[darthdavid]

I had in mind having it self-accreate, if possible, because that way you could use just about anything for fuel. Possibly even feed the ship's sewage line into it or something, anything with matter would do.

Don't feed it the sewage line. That can be put to much better use by using it for water reclaimation and feeding a hydroponic system (which can help provide atmosphere as well as food).

[TheBlackCat]

It would be a bit difficult to feed. If my calculations are correct you are looking at an event horizon of about 2.7*10^-18 m, or 2.7 attometers. That is about 0.056% the diameter of a hydrogen atom.

[Junghalli]

It would be a bit difficult to feed. If my calculations are correct you are looking at an event horizon of about 2.7*10^-18 m, or 2.7 attometers. That is about 0.056% the diameter of a hydrogen atom.

Sounds like the atom smasher method will be the way to go then.

I wonder how much fuel it'll consume every day...

[Surlethe]

It depends on the size of the tub. If it's a really, really small tub, then yes. Otherwise, it would take a while for it to pull the gas in as a matter of gravity (though I wonder what role the gas' pressure would play on it? That sounds like an interesting chemistry problem).

So basically you want a very, very small "feeding chamber" into which gas is continuously forced at high pressure?
I figured on using a high pressure gas because that way more molecules were likely to wander close enough to it to be sucked in.

Yes. Given TheBlackCat's calculations, though, it seems that your feeding chamber would have to be very small indeed. The Newtonian gravitational acceleration field of the black hole is something like 1.3e-1/r^2 m/s/s; to have a significant inward acceleration, you'd want a radius of a half meter or less. I'm not sure how the relativistic gravity varies from the Newtonian gravity as you get close to the hole.

You're also going to have to worry about collecting the energy of the black hole, since you're surrounding it with high-density gas.

[TheBlackCat]

At the very least you would probably want a liquid, preferably water or mercury or some other high-density liquid. You can never get a gas to have density anywhere near as high as its liquid state, and as you increase density you increase the chance that a particle will collide with your black hole at an given point in time. So you want something that will flow, but is also relatively dense. Also, liquids tend to have less linear velocity than gasses, meaning that the black hole is more likely to capture a liquid particle than a gas one (since the gas particle would have more velocity and thus can get closer to the black hole and still escape its graivity well). I think that would probably be the best bet.

[Kuroneko]

That completely ignores the fact that the radiation from a black hole that size would quickly turn its surroundings to plasma.

[TheBlackCat]

That would complicate matters. How exactly could you get anything to go into it, then? I would be extremely suprised if we could aim a particle beam preciely enough that the massive energy output wouldn't deflect it. That is completely ignoring the problem of making a particle beam with a high enough current to sustain the thing in the first place.

[Patrick Degan]

The one real requirement is to feed in enough material to offset the singularity's decay rate. Once you have that balancing act established, you can maintain it indefinitely.

For example, a 3500 metric ton black hole will have a lifetime of just marginally over one hour. A matter-feed of one ton per second will allow you to maintain the singularity for as long as you have material available to feed it. One solution Jerry Pournelle once suggested would be to contain yon wee beastie within a solid shell of very dense material and to simply allow the thing to feed on it. One problem of course is that you'll need to carry around a 31.5 million metric ton mass simply to maintain the singularity for a year.

A black hole of ten times that mass will last for 42 days, so the problem is somewhat simplified given its proportionately slower decay rate which would allow you to "refuel' with raw material periodically without the risk of the sigularity shrinking past a sustainable radius. The power output would also be fairly decent, at 2.91E17 watts. Assuming a 3% conversion efficency, that gives your starship the equivalent power of two 1MT thermonuclear devices detonating every second.

Of course, there are those pesky tidal forces and gamma radiation levels to deal with.

[LaCroix]

So, long story short:

You have a singularity (any given size), and it outputs a rather fixed amout of energy as it decays (use it or loose it).

If you dump matter into it, you get a short burst of energy and some increase in singularity mass.

So, all you need is a bit of neutronium star in the tank and off you go!

Sounds neat!