Black holes as heat sinks

Cooling in space is a well known difficulty. There are many unpleasant consequences like no stealth in space, difficult space battles which turn into a short wars of attrition (because you have to either pack your radiators, rendering them useless, or expose them, rendering them vulnerable), and many other complications. This is not only a problem with starships, but also with planets: even Kardashev type I civilization will run into problems keeping their cool if their energy usage on one planet already makes them a type I civilization.

But what if one considers using a black hole as a heat sink?

It seems pretty straightforward to just deposit the waste heat into the black hole, which would have a negligible increase on its mass. However, this seems to be burdened with a bunch of problems which should be addressed:

• Keeping the black hole in place. They are not really objects you can simply grab and hold. But perhaps a charged black hole (Reissner"“Nordström or, perhaps even better, Kerr"“Newman black hole) could be held using some sort of magnetic confinement.
• Black holes of any reasonable mass and sufficiently small gravitational field in their reasonable proximity have a very small Schwarzschild radius. Therefore, some precise aiming would be required and the question is whether this is possible to do with the waste heat.
• Hawking radiation. Planets depositing their waste heat in black holes probably wouldn't suffer from this problem, but a problem would arise when trying to downsize to for spaceships. Any reasonably small black hole would emit too much Hawking radiation which would make it too hot to be of any use as a heat sink. Using a black hole temperature calculator, it is easy to see that a black hole with a temperature of cozy $300$ K will have a mass of over $4\times10^{20}$ kg, which is almost half the mass of Ceres - plausible for planets, but not so much for spaceships (unless we are talking about something that can be easily confused for a moon). But perhaps using an extremal black hole could help since it should not emit the Hawking radiation.

Can these issues (and perhaps some other relevant key issues, overlooked in the list) be resolved to make a use of a black hole as a heat sink?

If yes, how?

posted over 5 years ago

Danijel‭

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