Author Topic: Would cooling convert dark matter to Hawking radiation?  (Read 1939 times)

Offline KelvinZero

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My understanding is that dark matter tends not to get hoovered up by black holes because it does not form accretion disks. Unless it hits the black hole pretty much dead on, it will just speed up momentarily and then continue on its merry way.

A corollary to this may be that dark matter does not have to overcome any of the usual phenomena that prevent normal matter from collapsing.

So Im speculating that if we ever did find a way to interact with dark matter, even slowly, it could be a convenient power source. Just cool it and it would easily form tiny black holes that instantly evaporate via Hawking radiation.

Does anyone know a reason why this would not turn out to be the case? My understanding is that due to quantum mechanics when you cool something its position becomes more fuzzy. (the more accurately you measure velocity, the less you know about position etc). Would this rule out this technique even without knowing specifics dark matter actually is?

Online Nilof

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Re: Would cooling convert dark matter to Hawking radiation?
« Reply #1 on: 12/16/2015 05:42 am »
Sure, but there'd be a lot of ifs.

For example, if Dark Matter is composed of Fermions, this won't work, because the repulsive forces in ordinary matter are due to the Pauli exclusion principle rather than the electromagnetic force.

Then there'd be the matter of gathering DM from enormous volumes of space - much larger than our solar system. Then you'd need to figure out how to cool it and reliably compress it in a volume smaller than a femtometer. That is, unless the dark matter already consists of primordial black holes with masses on the order of asteroids, which hasn't been definitively ruled out.

This doesn't mean that making black holes is impossible though, just extremely hard. Other ways to make them would be with a spherical shell of gamma ray lasers with perfect optics. Or you might be occasionally produce semi-stable black holes in a solar system sized particle accelerator. Either way it'd probably be in the realm of things a type-2 civilization would do.

If we go even more firmly into the realm of science fiction, making small black holes may be the kind of thing that would be much easier for a neutron star-based civilization like the Cheelas in Dragon's egg. An evaporating black hole may be the only practical engine for a launch vehicle designed to lift off from a neutron star. Or it may turn out to be an extremely suicidal idea, possibly being the cause of the gamma rays bursts we see from SGR 1806-20 ;D .
« Last Edit: 12/16/2015 05:42 am by Nilof »
For a variable Isp spacecraft running at constant power and constant acceleration, the mass ratio is linear in delta-v.   Δv = ve0(MR-1). Or equivalently: Δv = vef PMF. Also, this is energy-optimal for a fixed delta-v and mass ratio.

Offline KelvinZero

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Re: Would cooling convert dark matter to Hawking radiation?
« Reply #2 on: 12/20/2015 09:02 am »
I wasn't saying it would be fast, that would of course require actual numbers. I meant there would be no particular force to overcome, unlike things like fusion, let alone compressing matter into a black hole.

I knew that neutron stars were prevented from collapse from 'quantum degeneracy pressure' rather than electromagnetic forces but I had glossed over the difference. I had assumed any form of interference meant you could form accretion disks. Does the first not allow particles to interfere with each other and lose velocity? Is it a specific property of electromagnetic forces that they can leak energy away, eg as photons?




Offline IRobot

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Re: Would cooling convert dark matter to Hawking radiation?
« Reply #3 on: 12/20/2015 09:59 am »
Sure, but there'd be a lot of ifs.

You can start by the big "IF". "IF" Dark Matter exists.

It is still an unproven theory.

Offline KelvinZero

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Re: Would cooling convert dark matter to Hawking radiation?
« Reply #4 on: 12/20/2015 11:21 am »
Sure, but there'd be a lot of ifs.

You can start by the big "IF". "IF" Dark Matter exists.

It is still an unproven theory.

Now, I think it's a little early to start imposing roles on it, don't you?  :)

Please treat this as hypothetical. Even if you resent the establishment view of dark matter you should be able to just have fun speculating on the properties of something with mass, inertia but no known interaction with itself. Nilof's objections are great because at the same time that they may rule out this application they could point to possible tests of dark matter.

(I had a pet theory of dark matter being holes in otherwise fairly evenly distributed clouds of gravitationally repulsive particles, but I assume people have already considered that)

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