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posted by requerdanos on Sunday January 24, @12:55PM   Printer-friendly [Skip to comment(s)]
from the no-rush-though dept.

Could we harness energy from black holes?:

A remarkable prediction of Einstein's theory of general relativity -- the theory that connects space, time and gravity -- is that rotating black holes have enormous amounts of energy available to be tapped.

[...] [Now] physicists Luca Comisso of Columbia University and Felipe Asenjo of the Universidad Adolfo Ibáñez in Chile have found a new way to extract energy from black holes by breaking and rejoining magnetic field lines near the event horizon, the point at which nothing, not even light, can escape a black hole's gravitational pull.

"Black holes are commonly surrounded by a hot 'soup' of plasma particles that carry a magnetic field," said Comisso. "Our theory shows that when magnetic field lines disconnect and reconnect in just the right way, they can accelerate plasma particles to negative energies, and large amounts of black hole energy can be extracted."

The U.S. National Science Foundation-funded research results could allow astronomers to better estimate the spin of black holes and possibly discover a source of energy for the needs of an advanced civilization, Comisso said.

[...] "Thousands or millions of years from now, humanity might be able to survive around a black hole without harnessing energy from stars," Comisso said. "It is essentially a technological problem. If we look at the physics, there is nothing that prevents it."

Journal Reference:
Luca Comisso, Felipe A. Asenjo. Magnetic reconnection as a mechanism for energy extraction from rotating black holes, Physical Review D (DOI: 10.1103/PhysRevD.103.023014)


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  • (Score: 0) by Anonymous Coward on Sunday January 24, @01:02PM (20 children)

    by Anonymous Coward on Sunday January 24, @01:02PM (#1104465)

    > ... there is nothing that prevents it.

    Except that anything in proximity to a black hole also turns into a "hot 'soup' of plasma particles".
    And/or is torn apart by tidal forces?
    Or ??

    • (Score: 0) by Anonymous Coward on Sunday January 24, @01:05PM (2 children)

      by Anonymous Coward on Sunday January 24, @01:05PM (#1104468)

      I didn't even know we were actually sure black holes existed. Did someone get an image of one yet?

      • (Score: 2) by martyb on Sunday January 24, @01:46PM

        by martyb (76) Subscriber Badge on Sunday January 24, @01:46PM (#1104472) Journal

        I didn't even know we were actually sure black holes existed. Did someone get an image of one yet?

        Yes, apparently: Black Hole Image Makes History; NASA Telescopes Coordinate Observation [nasa.gov]

        See, also our previous coverage at: Event Horizon Telescope Team Releases First Image of a Black Hole [soylentnews.org]

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      • (Score: 2) by HiThere on Sunday January 24, @05:33PM

        by HiThere (866) on Sunday January 24, @05:33PM (#1104508) Journal

        Depends on precisely what you mean. There are certainly things that look pretty much like a black hole should look, but they might have a slightly different theoretical classification. There are arguments about whether there is really a singularity at the center, etc. The edges, however, would look sufficiently the same that we can't tell.

        So there's something in various places that looks just like a black hole would look, but theorists are arguing about details of the classification based on things we can't detect (or can't detect yet, anyway).

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    • (Score: 2) by takyon on Sunday January 24, @01:37PM (13 children)

      I think it's possible to approach a black hole if it's supermassive and doesn't have a death trap of hot plasma moving around at light speed near it.

      How to harness gravitational energy from a real life black hole? That's somebody else's problem.

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      • (Score: 2, Funny) by The Mighty Buzzard on Sunday January 24, @02:03PM

        It's Hole of Color, you insensitive clod!

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      • (Score: 4, Informative) by Immerman on Sunday January 24, @02:23PM (11 children)

        by Immerman (3985) on Sunday January 24, @02:23PM (#1104480)

        As I recall, the more massive the black hole, the lower the tidal forces as you approach the event horizon - sufficiently massive and you could actually cross the event horizon without being torn apart by tidal forces. The loss of any outflowing causal connections would presumably dissolve you anyway, but hey, at least you wouldn't be spaghettified.

        If you're just looking to get close though, in many ways smaller is better - e.g. if you magically compressed Phobos into a black hole, the event horizon would be miniscule, and from a couple dozen meters away it'd provide gravity comparable to Earth's with less tidal weirdness than a modest-sized rotating space station. If you were orbitting so that only tidal forces are an issue, you could get within a few meters without too much discomfort, and equipment with a small radial size could get within a few hands without needing anything fancy to resist the tidal forces. If you're playing with the interaction of force-fields, that's probably plenty close enough. Though with such a small event horizon you might not be able to exploit much.

        • (Score: 3, Interesting) by stormwyrm on Sunday January 24, @02:29PM (8 children)

          by stormwyrm (717) Subscriber Badge on Sunday January 24, @02:29PM (#1104482) Journal
          If Hawking radiation is real though, a small black hole like that though would hardly be black: it would in fact be white-hot and radiating strongly in gamma radiation, which would be a hell of a lot easier to harness. It would be less than the size of a proton though, and perhaps the simplest way way to get it to where you need it to be would be to tow a large mass in front of it, sort of like a carrot leading a donkey as Hawking himself put it.
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          • (Score: 4, Informative) by Immerman on Sunday January 24, @08:51PM (7 children)

            by Immerman (3985) on Sunday January 24, @08:51PM (#1104549)

            Phobos isn't quite that small, it's still much too much to put out a lot of power. According to https://www.vttoth.com/CMS/physics-notes/311-hawking-radiation-calculator [vttoth.com]
            a black hole of Phobos' mass (10^16kg) would have an effective
            - temperature of 12 million K
            - diameter of 30 pm (about 1/3 the diameter of a hydrogen atom, or 36,000x the diameter of a proton)
            - total power output (luminosity) of about 3.6W
            - and thanks to the low power output, would outlive the stars by many orders of magnitude.

            So basically, blazing hot, but with such a tiny surface area that it doesn't actually radiate much power. However, you could potentially use it as the core of a mass-energy converter, feeding it any scrap material as a fuel vastly more energy dense than fusion. Which might actually be more convenient than a radiant black hole, since you would have total control over the power output.

            Then again, if you've got the ability to create artificial black micro-holes it's probably far more useful to create something small enough to output a more useful amount of baseline power on its own - at 10^11kg (about 500 cruise ships) it'd be putting out 35GW, and still last for a couple billion years.

            • (Score: 0) by Anonymous Coward on Monday January 25, @06:57AM (1 child)

              by Anonymous Coward on Monday January 25, @06:57AM (#1104635)

              so how do you get a hold of a tiny black hole?
              I always thought it would be good to give it an electric charge and then you can literally get a handle on it... but it seems like it's a very dangerous thing to have around.

              • (Score: 2) by Immerman on Monday January 25, @03:01PM

                by Immerman (3985) on Monday January 25, @03:01PM (#1104728)

                Well, electro-magnetics and gravity are the ONLY forces that act at human scales (physical contact = electrostatic repulsion of electron clouds), so really your only options are giving it an electrostatic charge so you can manipulate it with charges and magnetic fields, or just relying on its mass, tugging it around using an outside mass as a "lure".

                Either way, the big danger would be making sure nothing got too close - from an appreciable distance away (say, at the distance where the original surface had been), the gravitational effects will be no different than the original normal mass.

            • (Score: 2) by Muad'Dave on Monday January 25, @01:01PM (4 children)

              by Muad'Dave (1413) on Monday January 25, @01:01PM (#1104689)

              diameter of 30 pm ... would outlive the stars by many orders of magnitude.

              I thought tiny black holes evaporated [briankoberlein.com].

              • (Score: 2) by Immerman on Monday January 25, @02:45PM (3 children)

                by Immerman (3985) on Monday January 25, @02:45PM (#1104721)

                They do - but the smaller they are, the greater the power output, and thus the faster they lose mass. The tiny ones with atom-scale masses that might be produced at the LHC would evaporate instantly. But Phobos is still pretty massive - at ~10km across it's still a good sized mountain.

                Try the calculator, it's fun to play with, just put in the mass and it'll tell you size, lifespan, luminosity(=power output), etc. in whatever units you want https://www.vttoth.com/CMS/physics-notes/311-hawking-radiation-calculator [vttoth.com]

                Some examples around the tipping point:
                Cruise ship (200e6kg): 7e15W, 32y
                Olympic-sized swimming pool (2.5e6 kg): 5.7e19W, 22 minutes
                40ft shipping container, filled to max (35e3kg): 3e23W, 3ms

                Of course, that assumes both that we properly understand Hawking radiation, and that there is no other quantum weirdness that starts messing with black holes smaller than an atom.

                • (Score: 2) by Immerman on Monday January 25, @03:04PM (2 children)

                  by Immerman (3985) on Monday January 25, @03:04PM (#1104729)

                  Oh, and just to put that power output in context:

                  That cruise ship would be putting out roughly 4x as much power as reaches the entire Earth from the sun.

                  The shipping container would be putting out almost 1/1000th of the sun's total power.

                  • (Score: 2) by Muad'Dave on Tuesday January 26, @12:32PM (1 child)

                    by Muad'Dave (1413) on Tuesday January 26, @12:32PM (#1105099)

                    Thank you for your informative replies to my questions!

                    • (Score: 2) by Immerman on Tuesday January 26, @02:16PM

                      by Immerman (3985) on Tuesday January 26, @02:16PM (#1105124)

                      You're welcome. You got me curious as to where exactly the tipping point was.

        • (Score: 2) by Muad'Dave on Monday January 25, @12:41PM (1 child)

          by Muad'Dave (1413) on Monday January 25, @12:41PM (#1104680)

          if you magically compressed Phobos into a black hole ... it'd provide gravity comparable to Earth's ...

          Wouldn't its gravity be exactly that of Phobos? Just because it's concentrated doesn't mean it would increase.

          • (Score: 2) by Immerman on Monday January 25, @03:19PM

            by Immerman (3985) on Monday January 25, @03:19PM (#1104734)

            At any given distance you would be correct, but gravity acceleration varies with distance from the center of mass according to the inverse square law: g = G*m/r^2

            When we talk about the gravity of a planet, we're talking at the surface - a.k.a. the point of maximum gravity. Fly upwards, and you're getting further away, so gravity diminishes. Dig under the surface and gravity starts diminishing again, since you're also getting pulled upwards by the mass above you.

            But since a black hole is far tinier than a normal object of the same mass, you can get far closer. Get 10x closer, and gravity gets 100x stronger. For a small black hole you could enclose it in shells of various sizes, and each shell would have a different surface gravity based on its distance. The closer you got, the stronger the pull would be, and also, the stronger the tidal forces: your feet would be closer than your head, and thus be pulled more strongly.

    • (Score: 5, Informative) by ElizabethGreene on Sunday January 24, @04:08PM (2 children)

      by ElizabethGreene (6748) on Sunday January 24, @04:08PM (#1104498)

      The accretion disk around a black hole has a significant amount of rotational energy. As that matter approaches the event horizon that matter moves (conservation of angular momentum) faster and faster until it begins emitting remarkable amounts of energy. Most of that energy is emitted (as gamma rays and x-rays) perpendicular to the accretion disk. It's not coherent light, but it's collimated enough that it can be harvested at significant distances from the black hole where tidal forces aren't a significant issue. Hawking radiation is also generated, but it is not concentrated at the poles. It is, by definition, random.

      If we don't discover a bunch of new physics that changes the game then it's likely that small black holes will be very valuable to Kardashev type three civilizations. They are a very efficient way to convert mass into energy. I hope that one day we figure out how to manufacture them. It would allow us extend the life of our civilization beyond the stellar age.

      • (Score: 2) by RedGreen on Sunday January 24, @04:48PM (1 child)

        by RedGreen (888) on Sunday January 24, @04:48PM (#1104504)

        "t would allow us extend the life of our civilization beyond the stellar age."

        I will take extending it beyond the human age, until we solve that one the stellar age means nothing....

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  • (Score: 2) by legont on Sunday January 24, @01:25PM (8 children)

    by legont (4179) Subscriber Badge on Sunday January 24, @01:25PM (#1104470)

    they can accelerate plasma particles to *negative* energies

    Looks like a black hole is a good candidate for an Alcubierre drive energy source.

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    • (Score: 0) by Anonymous Coward on Sunday January 24, @02:03PM (6 children)

      by Anonymous Coward on Sunday January 24, @02:03PM (#1104476)

      it's not *that* kind of negative energy.
      abstract calls it "negative relative to infinity", which is not a term I'm familiar with, but it looks like a specific notion that's meaningful in the context of spinning black wholes.

      as far as I know, the Alcubierre drive requires negative absolute energy, i.e. negative rest mass.

      • (Score: 5, Interesting) by Immerman on Sunday January 24, @02:47PM (5 children)

        by Immerman (3985) on Sunday January 24, @02:47PM (#1104485)

        Yeah, I'm not sure what they're talking about either, but possibly it's related to the way gravitational potential energy is normally measured from infinity, which is the only common reference point shared by all contexts. E.g. at infinite distance, with no gravitational interaction, we say there's zero gravitational potential energy between objects, while at any real distance the potential energy is negative, perfectly canceling the kinetic energy of an object traveling at escape velocity.

        And yeah, for an Alcubierre drive you need negative absolute energy, because you need to bend space in the opposite direction as normal mass: to invoke the common (though deeply flawed) "stretched rubber sheet of spacetime" analogy of gravity, you're trying to actually stretch the sheet upwards, so that things fall away from the source, rather than downwards so that they fall towards it. And no clever arrangement of "downward-stretching" (positive) mass energy can generate a net "upwards stretching" effect.

        At least, you do if you want to travel at FTL speeds. There was a recent paper analyzing the concept at sub-light speeds, and apparently no exotic matter is needed when you're not trying to travel faster than causality. Of course, without FTL you lose the original motive, but you still have an inertialess, reactionless drive combined with a tunable time dilation field - so it could still be incredibly useful while becoming theoretically possible to build using only normal matter.

        • (Score: 2) by choose another one on Sunday January 24, @03:55PM (4 children)

          by choose another one (515) on Sunday January 24, @03:55PM (#1104495)

          Of course, without FTL you lose the original motive, but you still have an inertialess, reactionless drive combined with a tunable time dilation field - so it could still be incredibly useful while becoming theoretically possible to build using only normal matter.

          Does it still completely destroy the destination star system on arrival?

          • (Score: 2) by Immerman on Sunday January 24, @08:59PM (3 children)

            by Immerman (3985) on Sunday January 24, @08:59PM (#1104550)

            I can't imagine any way even an FTL Alcubierre drive could accomplish that - unless maybe you were to vaporize the phenomenal mass-energy of your warp field/engine itself in a tight beam, which would be kind of ridiculous. You don't vaporize an airplane upon landing, you just reconfigure it a bit to let you out.

            • (Score: 2) by choose another one on Monday January 25, @04:22PM (2 children)

              by choose another one (515) on Monday January 25, @04:22PM (#1104752)
              • (Score: 0) by Anonymous Coward on Monday January 25, @06:06PM

                by Anonymous Coward on Monday January 25, @06:06PM (#1104786)
                Workaround:
                1) point the destructive cone at a direction away from your destination.
                2) Do stuff to untrap the high energy particles before they build up to unsafe levels - e.g. go to sublight speeds.

                Bonus points if you successfully create another universe on your arrival.
              • (Score: 2) by Immerman on Monday January 25, @06:13PM

                by Immerman (3985) on Monday January 25, @06:13PM (#1104793)

                Oh, right, I do remember that now. I believe later analysis suggested that most particles and radiation wouldn't be trapped within the field, instead passing through it to cook the passengers.

                But assuming the field is intense enough to create an event horizon, (though that would likely have issues with stopping) - you're talking about trapping roughly the quantity of mass-energy that occupied the full volume of the projected flight path at one single instant. Even assuming all the matter was torn apart and converted to energy, I don't think you're anywhere near the amount of energy necessary to destroy a star or probably even a planet - though you probably want to watch out for spaceships and stations, and might do some serious ecosystem damage if you blasted a life-bearing world.

                Let's see, some numbers:

                For convenience, lets say the warp field is about 18m across (1000m^2 cross section) Which is probably HUGE since as I recall a warp-bubble is TARDIS-like, with the size of the interior of the bubble being independent from the size of the exterior, and the energy requirements are based primarily on the external size.

                So, lets say we fly to the nearest star, sweeping out a straight cylinder of 4light years * 1000m^2 = 10^19m^3.

                Our sun is within the Local Bubble, an areas of hot interstellar medium with a density of about 1 atom per cm^3, with the nearest rim about 200 light years away - so I'll use that as the basic density. 1 (hydrogen) atom/cc = 1million atoms per m/3. Divided by Avogadros number to convert to mass = 1.7e-18 g/m^3

                So the total mass swept up while flying between stars = ~17kg = 1.6e18 J of energy

                Compared to the 1.7e17W of solar power constantly hitting the Earth, it would be about 10 seconds worth of solar energy. Released as a short enough burst that completely hits the planet that could probably do a lot of damage, but it's not going to vaporize the thing. Much less a star: the energy amounts to only a few picoseconds of our sun's energy output.

                Or, let's boil water with it: it takes 2257J to boil one cc of water (without heating it), so 1.6e18J is enough to boil a cube of 100C water that's 891m on a side. Nothing to sneeze at, but not all that much in the grand scheme of things.

    • (Score: 4, Funny) by VanessaE on Sunday January 24, @03:59PM

      Too late. The Romulans already beat you to it.

      (okay okay, it's a singularity, not a black hole, but close enough)

  • (Score: 2) by SemperOSS on Sunday January 24, @05:57PM

    by SemperOSS (5072) on Sunday January 24, @05:57PM (#1104510)

    … almost unlimited energy — if only you can survive the harvesting!   🕳   🡄 and that is a black hole seen from an angle.


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  • (Score: 3, Informative) by PinkyGigglebrain on Sunday January 24, @09:47PM (2 children)

    by PinkyGigglebrain (4458) on Sunday January 24, @09:47PM (#1104556)

    a really, really, REALLY long extension cord to get that energy back to Earth.

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    • (Score: 2) by EvilJim on Monday January 25, @02:19AM

      by EvilJim (2501) on Monday January 25, @02:19AM (#1104591) Journal

      and it will need to be a heavy duty core diameter. if only Tesla had figured out power transmission between planets instead of just around one.

    • (Score: 0) by Anonymous Coward on Monday January 25, @12:45PM

      by Anonymous Coward on Monday January 25, @12:45PM (#1104682)

      If habitats can be safely built in or near enough to the power-generation zone, we can exploit that to build a magnetosphere and real planet-style atmosphere...

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