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Dyson Sphere ‘Feedback’: A Clue to New Observables?

Although so-called Dysonian SETI has been much in the air in recent times, its origins date back to the birth of SETI itself. It was in 1960 – the same year that Frank Drake used the National Radio Astronomy Observatory in Green Bank, West Virginia to study Epsilon Eridani and Tau Ceti – that Freeman Dyson proposed the Dyson sphere. In fiction, Olaf Stapledon had considered such structures in his novel Star Maker in 1937. As Macy Huston and Jason Wright (both at Penn State) remind us in a recent paper, Dyson’s idea of energy-gathering structures around an entire star evolved toward numerous satellites around the star rather than a (likely unstable) single spherical shell.

We can’t put the brakes on what a highly advanced technological civilization might do, so both solid sphere and ‘swarm’ models can be searched for, and indeed have been, for in SETI terms we’re looking for infrared waste heat. And if we stick with Dyson (often a good idea!), we would be looking for structures orbiting in a zone where temperatures would range in the 200-300 K range, which translates into searching at about 10 microns, the wavelength of choice. But Huston and Wright introduce a new factor, the irradiation from the interior of the sphere onto the surface of the star.

This is intriguing because it extends our notions of Dyson spheres well beyond the habitable zone as we consider just what an advanced civilization might do with them. It also offers up the possibility of new observables. So just how does such a Dyson sphere return light back to a star, affecting its structure and evolution? If we can determine that, we will have a better way to predict these potential observables. As we adjust the variables in the model, we can also ponder the purposes of such engineering.

Think of irradiation as Dyson shell ‘feedback.’ We immediately run into the interesting fact that adding energy to a star causes it to expand and cool. The authors explain this by noting that total stellar energy is a sum of thermal and gravitational energies. Let’s go straight to the paper on this. In the clip below, E* refers to the star’s total energy, with Etherm being thermal energy:

When energy is added to a star (E increases), gravitational energy increases and thermal energy decreases, so we see the star expand and cool both overall (because Etherm is lower) and on its surface (because, being larger at the same or a lower luminosity its effective temperature must drop). A larger star should also result in less pressure on a cooler core, so we also expect its luminosity to decrease.

Image: Artist’s impression of a Dyson sphere under construction. Credit: Steve Bowers.

Digging into this effect, Huston and Wright calculate the difference in radius and temperature between the normal and irradiated stellar models. Work on irradiated stars goes back to the late 1980s, and includes the interesting result that a star of half a solar mass, if subjected to a bath of irradiation at a tempearature of 104 K, has its main sequence lifetime shortened by approximately half. The star expands and cools overall, but the distribution of the thermal energy causes its central temperature to increase.

A bit more on this background work: The 1989 paper in question, by C. A. Tout and colleagues, has nothing to do with Dyson spheres, but provides data on stellar irradiation of the sort that would be produced by proximity to a quasar or active galactic nucleus. Tout et al. worked on isotropic radiation baths at constant temperatures up to 104 K, finding that while the effects on stars whose energy is radiative are minor, convective stars increase in size. Keep in mind that cooler stars of low-mass are fully convective; hotter and more massive stars transport their energies from the interior through a radiative zone that forms and expands from the core.

Applying this to Dyson spheres, a star surrounded by technology would have light reflected back onto the star, while at the same time the sphere would become warm and emit thermal energy. I was intrigued to see that the paper gives a nod to Shkadov thrusters, which we’ve discussed in these pages before – these are stellar ‘engines’ using a portion of a star’s light to produce a propulsive effect. See Cosmic Engineering and the Movement of Stars, as well as Greg Benford’s look at the physics of the phenomenon, as developed by himself and Larry Niven, in Building the Bowl of Heaven.

Huston and Wright model how a Dyson sphere would affect the structure and evolution of a star, incorporating Dyson sphere luminosity as returned to the surface of the star. Each star is modeled from the start of its enclosure within the Dyson Sphere to the end of its main sequence lifetime. Beyond luminosity, the authors use Wright’s previous work on Dyson sphere parameters and his formulation for radiative feedback, while deploying a tool called Modules for Experiments in Stellar Astrophysics to assist calculations.

The authors consider stars in a mass range from 0.2 to 2 solar masses while varying luminosity fractions from 0.01 to 0.50. The effects of energy feedback on stars and the calculations on Dyson sphere properties produce absolute magnitudes for combined systems incorporating a central star and the Dyson sphere around it. From the paper:

Irradiated stars expand and cool. A Dyson sphere may send a fraction of a star’s light back toward it, either by direct reflection or thermal re-emission. This returning energy can be effectively transported through convective zones but not radiative zones. So, it can have strong impacts on low mass main sequence stars with deep convective zones which extend to the surface. It causes them to expand and cool, slowing fusion and increasing main sequence lifetimes. For higher mass stars with little to no convective exterior, the returned energy cannot penetrate far into the star and therefore has little effect on the star’s structure and evolution, besides some surface heating.

The effects are observationally significant only for spheres with high reflectivity or high temperatures – remember that Dyson assumed a sphere in the ~300 K area to correspond to a planet in the habitable zone. The authors combine the spectrum of the host star and the Dyson sphere into a ‘system spectrum,’ which allows them to calculate absolute magnitudes. The calculations involve the star itself, the interior of the sphere (both would be hidden) and the exterior of the sphere, which would be unobscured.

Wright has previously developed a set of five defining characteristics of a Dyson sphere, involving the intercepted starlight, the power of the sphere’s thermal waste heat, its characteristic temperature and other factors in a formalism called AGENT. The authors run their calculations on hot Dyson spheres and their opposite – cold, mirrored Dyson spheres that return starlight to the star without significant heating. Thus we go through a range of Dyson spheres intercepting starlight, including the familiar notion:

As the classical idea of a Dyson sphere, we can examine a solar mass star with low transmission of starlight through the sphere and a Dyson sphere radius of roughly 1 AU. We see that the feedback levels are very low and that the systems will appear, relative to a bare solar mass star, to be dimmed in the optical range and reddened in both optical and infrared colors.

Notice the range of temperatures we are talking about, for this is where we can expand our thinking on what a Dyson sphere might involve:

For our 0.2 and 0.4 M stars, feedback levels above roughly 1% cause at least a 1% change in nuclear luminosity; their effective temperatures do not significantly change. For our 1 and 2 M stars, feedback levels above roughly 6% cause at least a 1% change in the star’s effective temperature; their nuclear luminosities do not significantly change. Physically, these limits may correspond with a cold, mirrored surface covering the specified fraction of the star’s solid angle. For light-absorbing, non-reflective Dyson spheres, these feedback levels correspond to very hot spheres, with temperatures of thousands of Kelvin.

Dyson spheres in the latter temperature ranges are utterly unlike the more conventional concept of a civilization maintaining habitable conditions within the shell to gain not just energy but vastly amplified living space. But a hot Dyson sphere could make sense from the standpoint of stellar engineering, for feedback mechanisms can be adjusted to extend a star’s lifetime or reduce its luminosity. Indeed, looking at Dyson spheres in the context of a wide range of feedback variables is useful in helping jog our thinking about what might be found as the signature of an advanced technological civilization.

The paper is Huston & Wright, “Evolutionary and Observational Consequences of Dyson Sphere Feedback,” accepted at the Astrophysical Journal (abstract / preprint). The paper by Tout et al. is “The evolution of irradiated stars ,” Monthly Notices of the Royal Astronomical Society Volume 238, Issue 2 (May 1989), pp. 427–438 (abstract). For an overview of Dyson spheres and their background in the literature, see Wright’s “Dyson Spheres,” Serbian Astronomical Journal Issue 200, Pages: 1-18 (2020). Abstract / preprint. Thanks to my friend Antonio Tavani for the early pointer to this work.


{ 30 comments… add one }
  • Alex Tolley January 18, 2022, 14:23

    I gather this applies to Dyson spheres/swarms where the sunward facing side is similar to a planet, with an albedo. The surface my have an enclosed or unenclosed atmosphere.

    However, if that surface is to maximally extract the solar energy, it will have a face that is as close to 100% absorbing as possible for maximum energy extraction. The inhabitants could have an artificially projected sky if desired. Such a structure would not reflect visible light (or any em energy) back to the star, and from the perspective of the star, it would be radiating out into cold space.

    A consequence of this design approach is that the sphere/swarm need not be out at the HZ, but could be much closer to the star. The surface area would be smaller, the risk of structural failure might be raised and the consequences dire, but the tradeoff in resources needed to capture the energy and build the structure far lower.

    Perhaps an optimal approach is a close sphere/swarm of 100% light-absorbing material to extract the star’s energy, which is then transmitted to habitats wherever in the system they are located. Each habitat is therefore a high-energy using environment, and in aggregate still offers much space for each inhabitant if desired, with a living area far in excess of a planet. (They may look like O’Neill cylinders, but have many levels with the cylinder to offer surface space.)

    If the light trapping arrays are not 100% absorptive, there may be trade-offs in the reflectance impact on the star, with a possible optimum placement.

    • Alex Tolley January 18, 2022, 17:28

      Eqn 56.
      If the Dyson sphere (e.g. the collector) has a radius R = star’s radius, and Teff -> Tmin, then the efficiency approaches 1 (Ignoring the reflectance, etc).

      Therefore a collector design sitting as close to the star’s radius as possible to minimize mass, and able to convert the radiation so efficiently into a narrow beam (cable?) to power habitats and with a surface temperature of approaching Tmin (background temperature) would cause the star to be invisible, with no radiation emission to detect.

      Would ET simply collect and use its star’s energy for the lifetime of the star before it became a red giant, or would it try star lifting to reduce the star’s mass and have it burn for much longer?

      In extremis would a brown dwarf of class L or T be good candidates to build a Dyson sphere around for star-traveling ET? The radius is low, requiring less mass. The surface temperature is low enough to allow the use of ordinary matter to collect the radiation. The efficiency could still be high although output far lower than a main-sequence star. Lifetime might be high.

      The most exciting thing is that the star might be induced to move by expelling its surface as a narrow, high velocity, jet. A T-class BD with a surface temperature of 1300K or less could easily have its material ejected at one point in the shell, accelerated by the BD’s energy. The expanding jet might just be visible to telescopes, appearing as a comet-like jet with no obvious source, but moving across the background stars.

      [A BD with an engine capable of Isp = 100,000s, and consuming perhaps 10% of its mass for propellant would be traveling at 1000 km/s, far faster than the local stars. It would take about 1200 years to reach a star as close to Alpha Centauri is to Sol. Not bad if visiting other star systems over millions of years is the goal, with around 800 stars per my.]

      • Michael January 19, 2022, 2:42

        Best to let the star go through its natural phases and collect the matter afterwards, several red dwarfs masses worth are ejected.
        The stars also emit a lot more energy as they age and the white dwarf afterwards would still give off enomous amounts of energy for billions of years. It would also be easier to build rings and spheres as the size of the WD is much smaller.

    • Alex Tolley January 18, 2022, 17:41

      The most obvious parameter to me is the apparent size of the Dyson sphere. At 1AU, it has a radius of over 200x that of our sun. It would be very large, yet very cool if the T_ext is low, lower than a red giant. So the Dyson sphere might be the size of an RG, but with an apparently impossibly low surface temperature, emitting mostly radio waves rather than visible light or even IR.

      Are such an object’s large size and low temperature detectable and determinable by a telescope?

      • Alex Tolley January 19, 2022, 16:27

        To answer my question on detectability. It seems to me that the detection would be by occultation. It would look more like an asteroid occulting a star, than e.g. a dust cloud.

        The occultation time = (2R+2R*)/v
        where R = radius of the Dyson sphere, R* = the radius of the occulted star, and v = relative velocity of the Dyson sphere compared to the occulted star.

        Example. For a Dyson sphere 1 AU, occulting a sunlike star, at 1000 km/s relative velocity, the occultation time = ~ 42 hrs.
        Unlike a planetary transit, it would be a single event. Given the sphere’s size, the transit could well be a full occultation, with 100% light loss, that then reappears after some hours or days. The light curve would be unlike a planetary transit, with a slow light loss over R*/v time and a similar light increase as the occultation ends.

        The difficulty may be differentiating this event from an occultation by a nearby object such as an asteroid or KBO and a much more distant Dyson sphere.

  • Henry Cordova January 18, 2022, 14:53

    Has anyone ever taken a detailed and systematic look at the IRAS data looking for evidence of waste heat radiation from Dyson Spheres or other similar objects? Perhaps the wavelengths aren’t right, but it seems to me an all-sky survey of the infrared sky should reveal some evidence of these megastructures if they do indeed exist.

  • nat frey January 18, 2022, 15:13

    Maybe if the sphere was adjustable somehow, equipped with gargantuan window shutters, it could allow energy to reflect back onto the star, or let it pass through. If you had a star transitioning into an unruly phase of its life, this could be a way to keep it under control.

  • Geoffrey Hillend January 18, 2022, 18:20

    A lot of solar panels inside it might help. What could it be made out of? It might take more steal than is on the entire home world. Maybe mining the whole solar system and more.

    How far away from the star would it be built? It can be too close or it would over heat. Also how transparent is the Dyson sphere? Absorbing 100 percent of the light would put the outer solar system into total darkness or only star light.

    It would be tidally locked and forced to orbit with the star.

  • Brett Bellmore January 18, 2022, 21:09

    I’ve assumed that any statite array type structure would have a highly reflective interior.

    The reason for this is that a statite is supported by radiation pressure. But, if the statite array covers the entire sphere surrounding the star, and runs in thermal equilibrium, radiation absorbed on the inside equals radiation emitted from the outside. No lift!

    However, if the interior of the array is highly reflective, you first get twice the thrust from impinging photons, and second, you accumulate a photon ‘gas’ inside the array that increases the pressure roughly in proportion to the inverse of the absorption. Absorb 10% of the impinging radiation, it eventually accumulates to be 10 times as intense, and you end up with 90% of that providing net thrust.

    So the highly reflective statite array has much more lift, and can thus support much more infrastructure for a given stellar output.

    I was wondering how this would effect stellar evolution, and will have to think about the reasoning above.

    • David Claughton January 20, 2022, 20:30

      I was thinking along similar lines. As you say a Dyson sphere would be more like a statite than a satellite, since the gravitational attraction cancels out to zero it would not remain in a stable orbit but would be pushed around by solar flares and the like (as I understand it).

      I wonder if a Dyson sphere could take advantage of this reflection to dynamically correct this drift, perhaps by means of vast arrays of adjustable mirrors?

      • Brett Bellmore January 23, 2022, 9:16

        It absolutely could; Assuming complete closure, the interior is essentially filled with a photon gas, not a lot of control potential there, but the power generated could be used on the outside for photon thrusters.

        Of course, you want to use that power, but you could still get some positional control out of it by shifting load between different parts of the array for particular receivers.

        Most of the power would be arriving at the array in the form of light, but the solar wind would be carrying a lot of momentum. I wonder if a network of coils inside the array could tap that power while averaging out the thrust generated by the wind?

        By the way, a functioning statite array is actually a fairly low mass thing, since it has to be thin enough to be supported by photon pressure. I don’t think we’d even need to use up the whole asteroid belt to build one. And it would be a great source of power for interstellar flight.

        However, given the concerns about altering the behavior of the Sun, it might be wise to settle for just a band of statites, until we understand stellar dynamics better.

  • Mike Serfas January 18, 2022, 22:14

    One observable I didn’t see mentioned: What happens if things go terribly wrong and the Dyson sphere is left to break up and fall into the star? The energy it has stored in the outer layers of the star would seem ready to be released. Is there some type of nova or supernova that could be attributed to the failure of this sort of sphere?

  • Bernardo January 19, 2022, 12:05

    Acho que uma espécie super avançada nunca precisaria construir uma estrutura tão megalomaníaca apenas para geração de energia. Acho até que quanto mais avançados, mais discretos serão.

    And via Google Translate:

    I don’t think a super advanced species would ever need to build such a megastructure just for power generation. I even think that the more advanced they are, the more discreet they will be.

    • ljk January 19, 2022, 18:31

      The late Robert Bradbury did much, at least in some circles, to change the paradigm regarding Dyson Shells (not Spheres).

      Thankfully his original papers on the subject were saved here:



      Although this is a fictional universe, Orion’s Arm utilized a number of ideas Bradbury had about Dyson Shells. His most important breakout feature was seeing them as far more than just a new kind of dwelling for organic species. Dyson Shells could be beings unto themselves for a variety of reasons. Others have also envisioned Dyson Shells/Swarms as places to launch interstellar vessels using beamed power, or as weapons of immense power, reach, and destruction.


      Other references:



    • henry cordova January 20, 2022, 1:48

      Perhaps our enthusiasm for Dyson Spheres and other such megastructures stems from the psychological need of SETI enthusiasts to imagine such objects because they are detectable with our own level of technology. In a science embarrassed by a shortage of observational evidence, we all tend to fantasize on new sources and origins of data–it keeps us in business and justifies our own existence!

      Perhaps truly advanced civilizations quickly realize that it is relatively easy to reach a point where additional technology, expansion and industrialization doesn’t necessarily lead to more security, comfort, or satisfaction, however they may define that. Once you reach a point where your immediate needs are satisfied, you are safe from hazard, and your relations with your fellows and your neighbors are peaceful and enjoyable, you simply don’t need any more control over nature, especially when additional control always seems to provoke new problems.

      Consider an analogy; the businessman or tycoon who can never get enough wealth or power is as pathological a personality as the politician or ideology that wants to conquer the world and rebuild it in his image. Sure, exaggerated ambition is fine if you use it to do good (whatever THAT is), but what if you’ve already saved the world and all its inhabitants are living peaceful, happy and productive lives. We don’t need Dyson spheres any more than we need a Thirtieth Reich, a Socialist Worker’s Paradise, a Brave New World or yet another shining City on the Hill. The ultimate goal of cultural evolution may not be ever-increasing knowledge and power, but sufficient wisdom to know when to stop.

      A TRULY advanced civilization, after a useful and noble career, might just simply go into retirement. After ensuring its survival, its safety, and its immediate needs (whatever they may be) and perhaps added a bit of reserve capacity for possible emergencies, it might just kick back, pop a brew, and take up a hobby. That’s what I did when I retired and I’ve never been happier. I know that clashes with contemporary cultural values and prejudices, but hell, one of the reasons we study SETI is to question our own parochial superstitions. After all, the evidence we have so far seems to indicate our boosterism creates new problems faster than it solves the old ones.

      A truly advanced, well-adjusted and stable civilization might just view its gung-ho, go-getter, pathologically ambitious neighbor struggling to achieve Kardashev II status as quickly as possible a menace, a cancer to be nipped in the bud before it does something really stupid and ruins it for everybody else.

      At any rate, please forgive the harangue. I just think we need to remind ourselves that even if an advanced civilization is capable of building a Dyson Sphere, perhaps they may see no need , or exhibit any desire, to do so.

      • Alex Tolley January 20, 2022, 13:19

        Our assumptions of ET goals may make us seem like demented Ferengi to truly advanced civilizations.

        One feature of constant development is that it comes with increasing maintenance costs. As we are finding out, particularly in the US, failure to do the maintenance results in fragility. Things break unexpectedly and these failures can cascade.
        [Side note, I was just watching a lecture on the collapse of Mediterranean civilization in the 12th century BC. The argument given was that it was a confluence of events that caused the disruption of trade (e.g. Afghanistan tin for bronze) and the resulting domino-like collapse.]

        The other problem is that unless the civilization can achieve 100% recycling of everything, then waste will build up choking off maintaining the economy.
        [An analogy I once saw was a selection process for art students back in the 1970s. The candidates were kept in a room with some large blocks of polystyrene foam. Eventually, the foam blocks were reduced to tiny pieces that could no longer be combined in some way to demonstrate creativity. ] It may take a civilization a very long time to use up the rocks of a planet, but eventually, all they might be left with is sand (or concrete dust).

        Living small might be the wisest way to live well over the long term.

        Growing an economy as we do may make us like Blade Runner replicants – burning bright but expiring quickly. It takes but a few thousand years of constant growth to go from KI to KII status, and a similar time to become KIII (but the speed of light limitation prevents that growth rate). We seem incapable of steady-state zero-growth rate economics, requiring growth and collapse cycles instead. This may well prove disastrous in the long run. Other civilizations that endure may well have understood this and directed their energies in other directions.

        • Henry Cordova January 20, 2022, 17:15

          The first and last paragraphs of your very perceptive response to my comments summarizes the problem perfectly.

          The one thing all SETI enthusiasts seem to agree on is that “they” will be far advanced compared to us, at least, technologically. After all, we have only recently developed the science and technology to consider planning SETI searches.
          Presumably, they have been at it for millennia.

          Truly advanced civilizations would have identified the problem of destructive boom/bust cycles and unmanaged growth and come up with effective solutions a long time ago. In fact, that may very well be the definition of “advanced civilization”.

          “Demented Ferengi”. I love it.

  • Geoffrey Hillend January 19, 2022, 17:12

    Whether the Dyson Sphere could absorb all solar radiation 24/7 and still not over heat is another impracticable thing about it. I think I wrote on an earlier Dyson Sphere paper posted here on Centauri Dreams the same thing; Once a civilization figures out how to make a efficient nuclear fusion power plant, then the Dyson Sphere is obsolete. Ever solar power on Earth can do that, but scientists sometimes do thought experiments which extrapolate into the future using today’s technology or the technology of the past to solve our energy needs and population growth. Hawking thought the world’s over use of electricity would cause the Earth to become red hot, only a sheer speculation of course. Hawking 2001. This does not include progress and innovation.

    One could build quite a large solar power or fusion powered space station with only a small fraction of the mass and material of the Dyson Sphere or even a fleet of interstellar world ships.

  • Tom P. January 19, 2022, 19:36

    What if the aliens wanted to be really cold, to improve data processing, but still had uses for a lot of energy. I’m imagining a star surrounded by giant lenses, focusing the light outward for sails, or materials processing, or whatever. How would that change how the star would appear?

  • Carl Lumma January 20, 2022, 3:18

    Due to their low power density, I predict there are no Dyson spheres (or swarms) anywhere in the observable universe.

    • Michael January 20, 2022, 9:28

      ‘Due to their low power density, I predict there are no Dyson spheres (or swarms) anywhere in the observable universe.’

      Observable been the self contradicting word…

  • Michael Fidler January 20, 2022, 6:34

    Two ideas that may be worth looking into relating to civilizations that may not want to change the evolution of stars.
    1. What do we need energy for, the production of goods. Instead of sending people to live on Dyson spheres or colonies in space the best ecologically would be to send industries into space. Giant flat moons orbiting a sun would be stable and be able to use the photoelectric energy or internal fusion combined with AI to produce anything needed. This would leave the home worlds back to their natural unpolluted state with only electricity being produced from fusion for homes and vehicles. Products would be sent to the home world and terraformed worlds with vehicle that have ion magnetic fields so not to overheat the atmosphere. Material from dust asteroids and comets would feed the factories and an added benefit would take from the JWST of a cold sunless side having superconducting electronics. These may be visible via transits.
    2. Instead of enclosing stars why not gas giants and L,T and Y Brown dwarfs and rogues. Like; 2010: The Year We Make Contact, the ability to make a large surface area around such objects after causing collapse and long lived light and heat production. Small mini stars manmade. There may be billions of such objects with small signatures. Some may be visible in transits or microlensing.

    • Michael Fidler January 21, 2022, 2:19

      Well it looks like the Lithium 7 theft or “white petroleum” problem has been solved!

      Astronomers discover ancient brown dwarf with lithium deposits intact.


      The ETs must be mining the L7 to ignite the L and T brown dwarfs…
      Some place I have an image of the drop in L to T dwarfs and where are the rest hiding? Maybe we need to look a little closer at this very BIG anomaly and see if Dyson spheres can control the burn levels in the reignited L and T brown dwarfs…

      • Andrei February 5, 2022, 20:30

        This Lithium was found in the smallest of those brown dwarfs. This means that the object was too small to briefly ignite and shine as a small star shortly after formation. In the larger of the brown dwarfs this lithium is consumed from the nuclear process = it’s no anomaly or mystery.

  • Samuel January 20, 2022, 10:59

    Somewhat along what Barnardo suggested, a Dyson sphere even today seems antiquated. With metamaterial technology we know about today, I would think a civilization thousands of years in advance would be able to redirect most if not all of the sunlight from their sun into a specific area to use as they wished, without the need to create a massive sphere from other planets in their solarsystem.

    • Alex Tolley January 20, 2022, 19:51

      Metamaterials with perfect refraction could be made into lenses that could orbit the star, directing beams into space like terrestrial lighthouses. Depending on the number of such lenses, the star might appear to distant observers as though constantly emitting large flares (like M_dwarfs?). Civilizations efficiently use their star to signal to the cosmos “Here we are”, and yet we ignore them as “natural phenomena”. ;)

  • Andy Prada January 20, 2022, 19:46

    Ah, but for every Arisian, there is surely an Eddorian, is there not?

  • Mike Serfas January 21, 2022, 13:12

    The more I think about it, the more I feel like the aliens should go the other way and *remove* energy from the star.

    Suppose they set up shop around a nice bright class A star like Vega. They build a sphere that has a comfortable 250K equilibrium temperature and radiates infrared in all directions. When they send their space probes outward, they rely on that infrared radiation for energy, by means of radiating light at even colder temperatures. Being sphere builders, eventually these probes coalesce into a colder sphere. We’ll say the first sphere is a Class T Dyson sphere, and the outer one is a Class Y Dyson sphere based on their color/color temperature.

    Now the aliens are getting tired of wearing SPF 500 and getting cataract surgery every three months, so they hatch a plan to turn their blue star yellow. Naturally this involves building a Class G Dyson sphere, so that when they look up they no longer see a tiny blue star but a roughly Sun-sized sphere in angular terms that gives them a temperature still similar to Earth.

    Well, when they see what the power extracted by that sphere does to lower their energy bills, it’s not going to be long before they are building a Class F sphere. And after that they want a type A sphere, but their star is type A itself, and having the hot and cold reservoirs the same is no way to run a steam engine.

    But not to worry! Just build a space elevator/fountain/countercurrent exchanger, whatever you call this thingy, it sucks plasma from the inner surface of the class A sphere, pipes it to the Y sphere where they need the heat, and returns the same mass of condensate along the same path, minus deductions. (They probably had an ad hoc version of this before to transmute up all that Dyson sphere building material) Now they’re extracting extra energy from the star’s surface – cooling it, allowing it to contract inward. As I understand it, this actually increases the star’s surface temperature even as it shrinks, so now the class A sphere is delivering current, and they have some space underneath it to get working on their class B sphere…

    Now, all this is fiction: presumably the aliens would have a Dyson swarm of vehicles capable of navigating any environment from the outer system to the photosphere of the star, and integrate all the layers in a single swarm. But a monument of greed like a Dyson swarm should not settle for milk when there is beef on the menu. Artificially enhance the convection rate of the star, and it should start producing more fusion energy at the expense of its lifespan.

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