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A Dyson sphere around a black hole

(arxiv.org)
214 points SkyMarshal | 3 comments | 19 Aug 21 03:40 UTC | HN request time: 0.502s | source
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saagarjha ◴[19 Aug 21 05:02 UTC] No.28230503[source]▶
Better link: https://arxiv.org/abs/2106.15181

The results are fairly obvious: CMB and Hawking radiation provide almost zero power output, while an accretion disk and relativistic jets can provide a lot of power.

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kragen ◴[19 Aug 21 05:18 UTC] No.28230601[source]▶
Oh cool, CC-BY!

In theory you can get an arbitrary amount of power from Hawking radiation if you have a lot of very small black holes instead of just one big one. I feel like the stability of the negative-feedback control systems for their orbits might be important here, especially if they're orbiting something you care about like your home planet.

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m_mueller ◴[19 Aug 21 05:43 UTC] No.28230733[source]▶
As far as I understand, small black holes could be used as a super efficient energy storage („Kugelblitz“), but hardly as a source, assuming that primordial black holes are rare. Primordial black holes afaik are the only theorized origin of a sub stellar mass black hole at this stage of the universe‘s timeline.
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kragen ◴[19 Aug 21 06:50 UTC] No.28231105[source]▶
Yeah, making tiny black holes could be pretty challenging, but I feel like it's just an engineering challenge. Is there a fundamental reason I'm missing that you can't just build a really precise, solar-system-scale particle accelerator to slam together a lot of mass into a tiny space to make tiny black holes?
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1. jleahy ◴[19 Aug 21 07:14 UTC] No.28231216[source]▶
It’s just too much mass in too little space. It’s essentially the same requirement as fusion, but almost infinitely more difficult.

If you could make a fusion reactor almost infinitely better then it would produce a black hole which would immediately evaporate releasing more energy than you could ever imagine - but no way it can be done.

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2. sbierwagen ◴[19 Aug 21 07:27 UTC] No.28231303[source]▶
Hawking radiation propulsion has the perfect specific impulse: exhaust velocity is the speed of light. Black hole hawking radiation also is perfectly efficient: 100% of the mass is converted into energy. D-T fusion only converts 0.4% of the mass to energy.

There are many awful engineering problems of a black hole drive, but they're not so bad as to dismiss out of hand. See https://arxiv.org/abs/0908.1803v1

3. kragen ◴[19 Aug 21 08:39 UTC] No.28231661[source]▶
You know, if you asked Christiaan Huygens in 01671 about the possibility of detecting a 4-km-long tunnel getting shorter by a factor of one in a sextillion for a hundredth of a second, he surely would have doubted that it was possible. But it's only been 350 years, and when LIGO detected its first gravitational waves five years ago, that's precisely how it did it.

By contrast, there's ample reason to believe that black-hole power plants are possible. In fact, the spatial precision required is actually the same order of magnitude as that of LIGO, about an attometer. So we might not even have to wait 350 years for it.