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How could astrophysical jets, emitting matter from black holes be used as energy sources by a space-faring nation? How could they be able to collect and use this form of energy?

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    $\begingroup$ Photovoltaic panels. $\endgroup$
    – BMF
    Feb 9, 2020 at 16:49
  • $\begingroup$ What is the technology level of your space-faring nation? May they build astrophysical structures as large as solar systems? Are they voyaging nomads in a centureis-old, space-worn generation ships, technology not far off from our own? $\endgroup$
    – BMF
    Feb 9, 2020 at 16:52
  • $\begingroup$ Hi BMF for Monica, they are a space-faring nation which can build rather large structures but not as large as solar systems. Constructing a space station of tripple the size of Babylon 5 is possible but a big effort. Their technology is quite advanced approx. 250 years ahead of our own. $\endgroup$
    – at_
    Feb 9, 2020 at 21:35

2 Answers 2

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Stellar JetSail

This is basically a solar sail on steroids. Unlike solar sails, which rely on a relatively gentle wind of particles, you need something much more sturdy. Rather than trying to capture the relativistic particles, since most of them are ionized, you can simply try to steal some of their kinetic energy by setting up a large electrostatic field. Instead of a solid sheet of photon-absorbing material, you instead want a large thin wire grid through which you can pass current.

Inverse Ion Drive

Shooting ions through a charged grid at high speed is exactly the function of an ion thruster. If you already have high speed ions, then instead of speeding them up, you just want to slow them down and capture their momentum. So this "sail" is really like a giant ion drive operating in reverse. If you have materials sufficiently sturdy to survive the jet in the first place, then you can stack several of these sails in series. Each one might only capture a fraction of ion energy, but as they pass through each sail, they slow down and you steal more momentum. It may be possible to stack enough of them that the very last layer is a proper solar sail, where you can literally catch the ions to steal 100% of their momentum, and then dump them over the side (at 0 relative velocity, so you don't have to accelerate them as dead weight).

Parasitic Power

Of course, you need to charge your grids to actually interact with the ions usefully, and this takes power. But you can also harvest power as the ions move through a magnetic trap, which operates like a kind of linear particle accelerator in reverse. Thus, the jet can power both your ship and the ion grid.

Shielding

Of course, a relativistic jet is going to bombard any spacecraft with a pretty tremendous amount of energy. Probably the most sustainable way to survive this is to create a powerful magnetic field which simply diverts most of the ions around your ship proper (but not so much that they occlude the sail). Again, the magnetic field can itself be powered by the jet (though you need seed energy to power the shield before you enter the jet!).

Disposable One-Way

A simpler solution would be to just create a massive shield which can absorb/deflect 100% of the jet without fancy grids or generators or magnetic shields. Unfortunately, there may not exist any material which can withstand the power density involved. The most obvious solution would be to just get an adequately large asteroid as the shield, park your ship on the lee side, and push it into the jet, letting the asteroid ablate away until you reach your destination. Unfortunately, the asteroid is likely to get hotter and hotter, unable to dump enough energy to stop from melting into a metal plasma long before you reach your destination. But all of this depends on how far away you are from the jet, how collimated the jet is, etc.

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  • $\begingroup$ Wow. You are amazing. Thanks so much! $\endgroup$
    – at_
    Feb 10, 2020 at 14:36
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The Penrose mechanism - how to extract energy from a black hole

  • Throw an object with a certain trajectory into the black hole
  • Once in the ergosphere, break the object in two to give them a certain trajectory
  • is absorbed by the black hole decreasing its cinetic spead
  • gets out the ergosphere with a superior spead and a total energy superior to the mass energy of the original object.

enter image description here

https://arxiv.org/pdf/1510.06764.pdf

Also from what I see in the article, if you break the object in more than two pieces, the speed stacks with the number of object you throw into the black hole.

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    $\begingroup$ This is a good answer for how to extract energy from a rotating BH. But it doesn't address how to extract energy from relativistic jets. $\endgroup$
    – BMF
    Feb 9, 2020 at 18:29
  • $\begingroup$ @BMFForMonica Ok I kind of understand your comment but reading the wikipedia link of the op's question, you understand this is how relativistic jets aquire their energy right ? Transposing this BH - relativistic jets relation to a relativistic jets - space-faring nation is possible, Just do with relativistics jets what you would you do with BH ? Does it needs a proper technology described ? $\endgroup$ Feb 9, 2020 at 19:33
  • $\begingroup$ perhaps to the author of the question it matters. The OP still hasn't described the technology level of his worldbuilding. His space-faring nations might not be capable of coming anywhere near an energetic object like an accreting black hole. $\endgroup$
    – BMF
    Feb 9, 2020 at 19:42
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    $\begingroup$ @at_ Glad you like it. I don't know how much you want to go into hard sf, but you could imagine a technology gathering jet streams into some sort of (very) small black hole, these would be placed at different point into the solar system/galaxy creating a network for interstellar travel (using the same mecanism I describe). Do you follow me ? It means E0 is a spaceship with removable parts. I can elaborate in the answer if you want :) $\endgroup$ Feb 10, 2020 at 13:49
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    $\begingroup$ To precise my answer, it is not about energy creation. Energy is not really created, it is "extracted" or "transfered". This is why it is perfect for interstellar travel, you don't have to store it, you just use it for propulsion. The main issue is, how do I locate jet streams, and store it in a single location, like a black hole. $\endgroup$ Feb 10, 2020 at 13:59

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