I’m enjoying the conversation about Project Hephaistos engendered by the article on Dyson spheres. In particular, Al Jackson and Alex Tolley have been kicking around the notion of Dyson sphere alternatives, ways of preserving a civilization that are, in Alex’s words, less ‘grabby’ and more accepting of their resource limitations. Or as Al puts it:
One would think that a civilization that can build a ‘Dyson Swarm’ for energy and natural resources would have a very advanced technology. Why then does that civilization not deploy an instrumentality more sly? Solving its energy needs in very subtle ways…
As pointed out in the article, a number of Dyson sphere searches have been mounted, but we are only now coming around to serious candidates, and at that only seven out of a vast search field. Two of these are shown in the figure below. We’re a long way from knowing what these infrared signatures actually represent, but let’s dig into the Project Hephaistos work from its latest paper in 2024 and also ponder what astronomers can do as they try to learn more.
Image: This is Figure 7 from the paper. Caption: SEDs [spectral energy distributions] of two Dyson spheres candidates and their photometric images. The SED panels include the model and data, with the dashed blue lines indicating the model without considering the emission in the infrared from the Dyson sphere and the solid black line indicating the model that includes the infrared flux from the Dyson sphere. Photometric images encompass one arcmin. All images are centered in the position of the candidates, according to Gaia DR3. All sources are clear mid-infrared emitters with no clear contaminators or signatures that indicate an obvious mid-infrared origin. The red circle marks the location of the star according to Gaia DR3. Credit: Suazo et al.
We need to consider just how much we can deduce from photometry. Measuring light from astronomical sources across different wavelengths is what photometry is about, allowing us to derive values of distance, temperature and composition. We’re also measuring the object’s luminosity, and this gets complicated in Dyson sphere terms. Just how does the photometry of a particular star change when a Dyson sphere either partially or completely encloses it? We saw previously that the latest paper from this ongoing search for evidence of astroengineering has developed its own models for this.
The model draws on earlier work from some of the co-authors of the paper we’re studying now. It relies on two approaches to the effect of a Dyson sphere on a star’s photometry. First, we need to model the obscuration of the star by the sphere itself. Beyond this, it’s essential to account for the re-emission of absorbed radiation at much longer wavelengths, as the megastructure – if we can call it that – gives off heat.
“[W]e model the stellar component as an obscured version of its original spectrum and the DS component as a blackbody whose brightness depends on the amount of radiation it collects,” write the authors of the 2022 paper I discussed in the last post. The modeling process is worth a post of its own, but instead I’ll send those interested to an even earlier work, a key 2014 paper from Jason Wright and colleagues, “The Ĝ Infrared Search for Extraterrestrial Civilizations with Large Energy Supplies. II. Framework, Strategy, and First Result.” The citation is at the end of the text.
The recently released 2024 paper from Hephaistos examined later data from Gaia (Data Release 3) while also incorporating the 2MASS and WISE photometry of some 5 million sources to create a list of stars that could potentially host a Dyson sphere. In the new paper, the authors home in on partial Dyson spheres, which will partially obscure the star’s light and would show varying effects depending on the level of completion. The waste heat generated in the mid-infrared would depend upon the degree to which the structure (or more likely, ‘swarm’) was completed as well as its effective temperature.
So we have a primary Dyson sphere signature in the form of excess heat, thermal emission that shows up at mid-infrared wavelengths, and that means we’re in an area of research that also involves other sources of such radiation. The dust in a circ*mstellar disk is one, heated by the light of the star and re-emitted at longer wavelengths. As we saw yesterday, all kinds of contamination are thus possible, but the data pipeline used by Project Hephaistos aims at screening out the great bulk of these.
Seven candidates for Dyson spheres survive the filter. All seven appear to be actual infrared sources that are free of contamination from dust or other sources. The researchers subjected the data to over 6 million models that took in 391 Dyson sphere effective temperatures. They modeled Dyson spheres in temperature ranges from 100 to 700 K, with covering factors (i.e., the extent of completion of the sphere) from 0.1 to 0.9. Among many factors considered here, they’re also wary of Hα (hydrogen alpha) emissions, which could flag the early stage of star growth and might be implicated in observations of infrared radiation.
Image: IC 2118, a giant cloud of gas and dust also known as the Witch Head Nebula. H-alpha emissions, which are observed over most of the Orion constellation, are shown in red. This H-alpha image was taken by the MDW Survey, a high-resolution astronomical survey of the entire night sky not affiliated with Project Hephaistos. I’m showing it to illustrate how pervasive and misleading Hα can be in a Dyson sphere search. Credit: Columbia University.
I want to be precise about what the authors are saying in this paper: “…we identified seven sources displaying mid-infrared flux excess of uncertain origin.” They are not, contra some sensational reports, saying they found Dyson spheres. These are candidates. But let’s dig in a bit, because the case is intriguing. From the paper:
Various processes involving circ*mstellar material surrounding a star, such as binary interactions, pre-main sequence stars, and warm debris disks, can contribute to the observed mid-infrared excess (e.g. Cotten & Song 2016). Kennedy & Wyatt (2013) estimates the occurrence rate of warm, bright dust. The occurrence rate is 1 over 100 for very young sources, whereas it becomes 1 over 10,000 for old systems (> 1 Gyr). However, the results of our variability check suggest that our sources are not young stars.
Are the candidate objects surrounded by warm debris disks? What’s interesting here is that all seven of these are M-class stars, and as the authors note, M-dwarf debris disks are quite rare, with only a few confirmed. Why this should be so is the object of continuing study, but both the temperature and luminosity of the candidate objects differs from typical debris disks. The questions deepen and multiply:
Extreme Debris Disks (EDD) (Balog et al. 2009), are examples of mid-infrared sources with high fractional luminosities (f > 0.01) that have higher temperatures compared to that of standard debris disks (Moór et al. 2021). Nevertheless, these sources have never been observed in connection with M dwarfs. Are our candidates’ strange young stars whose flux does not vary with time? Are these stars M-dwarf debris disks with an extreme fractional luminosity? Or something completely different?
The authors probe the possibilities. They consider chance alignments with distant infrared sources, and offsets in the astrometry when incorporating the WISE data. There is plenty to investigate here, and the paper suggests optical spectroscopy as a way of refuting false debris disks around M-dwarfs, which could help sort between the seven objects here identified. Stellar rotation, age and magnetic activity may also be factors that will need to be probed. But when all is said and done, we wind up with this:
…analyzing the spectral region around Hα can help us ultimately discard or verify the presence of young disks by analyzing the potential Hα emission. Spectroscopy in the MIR [mid-infrared] region would be very valuable when determining whether the emission corresponds to a single blackbody, as we assumed in our models. Additionally, spectroscopy can help us determine the real spectral type of our candidates and ultimately reject the presence of confounders.
So the hunt for Dyson spheres proceeds. Various pieces need to fall into place to make the case still more compelling, and we should remember that “The MIR data quality for these objects is typically quite low, and additional data is required to determine their nature.” This layman’s guess – and I am not qualified to do anything more than guess – is that rather than Dyson spheres we are glimpsing interesting astrophysics regarding M-dwarfs that this investigation will advance. In any case, do keep in mind that among some five million sources, only seven show compatibility with the Dyson sphere model.
If Dyson spheres are out there, they’re vanishingly rare. But finding just one would change everything.
The paper on Dyson sphere modeling is Wright et al., “The Ĝ Infrared Search for Extraterrestrial Civilizations with Large Energy Supplies. II. Framework, Strategy, and First Result,” The Astrophysical Journal Vol. 792, Issue 1 (September, 2014), id 27 (abstract). The 2022 paper from Project Hephaistos is Suazo et al., “Project Hephaistos – I. Upper limits on partial Dyson spheres in the Milky Way,” Vol. 512, Issue 2 (May 2022), 2988-3000 (abstract / preprint). The 2024 paper is Suazo et al., “Project Hephaistos – II. Dyson sphere candidates from Gaia DR3, 2MASS, and WISE,” MNRAS (6 May 2024), stae1186 (abstract / preprint).
Ben Walmisleyon May 18, 2024 at 5:11
A sufficiently advanced technology is indistinguishable from natural phenomena when enough stars are examined!
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Edmund K.on May 18, 2024 at 12:41
My sense with these searches is that we are still looking for twentieth-century fantasies of what ET might look like rather than dealing with what is actually out there. The Dyson Sphere seems like a conceptual “scaling-up” of mid-century industrial society—very much a 1950s understanding of what an alien society might do (based on 1950s understandings of energy needs and how they might be satisfied). The failure so far of SETI—the fact that the universe doesn’t appear to resemble 20th-century sci-fi fantasies of an inhabited realm full of humanity analogues—surely calls for some recalibration of our expectations?
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henry cordovaon May 18, 2024 at 19:23
Please forgive me for reprising this comment to a previous thread, but I believe your own remarks are apt, and I wish to reinforce them further.
I don’t really expect any of these infrared anomalies will ever be found to be an artifact of an extremely powerful civilization, one operating on a scale involving entire planets, stars and planetary systems. Even if one can conceive of a civilization lasting long enough to develop such near-godlike powers, its difficult to come up with a reason why they would want to.
Our desire to speculate about such colossal powers is that we simply haven’t been able to explain away the embarrassing fact that much easier means of interstellar communication have so far failed to turn up. Instead, we fantasize about brooding, almost supernatural, intelligences hammering away at the forges of heaven creating…what? SETI enthusiasts are fascinated by technology, seduced by our own pathetic dabbling in those arts, and think of this sort of aggressive hyper-industrialism MUST be the sign of true intelligence, genuine civilization.
I suppose its not impossible, the universe is old enough and big enough to make almost anything possible, somewhere, sometime. But I suspect a truly wise and advanced culture would find less spectacular and disruptive hobbies, such as securing eternal life, security from cosmic catastrophe, true scientific understanding, or even deliberately searching for other species. Making bonfires of planets and harnessing the power of entire suns seems like an awful lot of sturm und drang. It makes sense to us mostly because we’re desperate for some sort justification of our own fantasies. We like to think of ourselves as an aggressive tribe of explorers, entrepreneurs and conquerors, and we can’t imagine anyone worthwhile not being the same. We listened for microwave signals and we didn’t find any (after listening for a whole half century!) So now we fantasize about Marioshka Brains, Dyson megastructures and Kardashev Kultures. Surely, they must have left some imprint on the cosmos.
I suspect intelligent civilizations are out there, but they are few and far between for the reasons I have spelled out previously. They are highly separated in space and time, and there is little incentive for any of them to expand indefinitely until they are capable of leaving a footprint that can be detected at galactic distances. Once they have reached a certain level of comfort and security they simply will have no need to continue expanding. and “progressing”. The few crazy enough to follow that psychotic path will eventually kill themselves off or stew in their own poisons.
Still, I welcome this interest in sifting through old astronomical catalogs and databases. Something of interest is bound to turn up, even if it isn’t evidence of technological overreach, but just some interesting little astrophysical process we haven’t stumbled onto yet.
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Robin Dattaon May 19, 2024 at 3:57
Sophistication in handling matter, energy, time and space will manifest itself in such minimized disruption of these that no disruptions may be detected. Or maybe dark matter and dark energy are their waste products, as suggested here many moons ago by Alex Tolley.
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Montieon May 18, 2024 at 8:46
According to the Bradbury M-Brain page using our own star as an example, a cloud of material could cover a star all the way out to the orbit if Neptune. That much material between star and cloud edge would make it no more visible than background radiation.
Was he wrong? Would IR still get through? Can not heat be directed away so as to not point at other stars?
–sincerely, Not A Real Scientist.
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Roberton May 18, 2024 at 11:37
It seems unreasonable to me that a truly advanced civilization would be interest in tapping the last joule of solar energy of it’s star over more exotic but convenient forms of energy such as fusion. Do what stars do but on your own terms. More likely it would be far in advance of fusion to some source we can’t even imagine yet. Yet, Sir Arthur C. Clarke did imagine something exotic in his books with monoliths exponentially multiplying over Jupiter blocking out its light and engineering its properties. Like a local Dyson Sphere but for another purpose. Perhaps as Sir Arthur suggested, it would appear like magic to us.
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Wojciech Jon May 19, 2024 at 7:50
There is no reason to assume such constructs would serve to only gather energy, besides other functions.
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Roberton May 19, 2024 at 16:38
I was originally going to make the point that attempts to hide a civilization from others would be futile if even humans with current technology can devise ways to detect them as demonstrated by the above paper.
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Ron S.on May 18, 2024 at 12:36
“5 million sources”
“1 over 10,000 for old systems”
“Seven candidates”
These number popped out at me. Despite my having eliminated much of the nuances of this data related to those quotes, the rough statistics seem underwhelming to me. If there are Dyson swarms/spheres, they must be very rare.
Robert: “It seems unreasonable to me that a truly advanced civilization would be interest in tapping the last joule of solar energy of it’s star over more exotic but convenient forms of energy such as fusion. ”
I agree. A civilization isn’t advanced if it must huddle around a campfire.
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Michaelon May 19, 2024 at 4:04
Ron, that’s is one huge camp fire ! There would be enough energy concentrated to throw huge vessels out into space at great velocities. But thinking about wether they are Dyson swarms or natural phenomenon I would tend towards the latter. The reason being is that if an advanced race were to build one around their host star surely they would build another one around the next nearest star. The candidates appear to be randomly about the sky with huge distances between them.
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Ron S.on May 19, 2024 at 16:43
Have you ever tried to transport a large electric generating station on a truck? A generator that can’t be moved is of very limited utility. I repeat: a civilization that can’t produce the power it needs where it’s needed is not advanced.
Yes, a star is big and powerful, but it’s still a campfire in this respect. Stay close if you need to stay warm! We aspired higher and found ways to generate power and cut the tether.
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Mike Serfason May 19, 2024 at 19:34
The term “Dyson” has been overused, I think, to the point where it introduces more confusion than clarity. In this case, the authors are looking for an excess of mid-IR, but surrounding stars that we can still see in UV and visible wavelengths. If the source is artificial, it is not a hermetic sphere, nor even a dense cloud that blots out the star, but merely a lot of space traffic – enough that, combining all the surface area, it starts to rival the star if you look at the right wavelength. If we assume interstellar travel remains hard, and colonizing new systems is slow, and the attention of the spacefarers is divided among dozens or hundreds of nearby systems, then we can readily imagine that the traffic around any nearby star would be many orders of magnitude less than the homeworld, and therefore invisible to this sort of survey. (Development might also be paused by a Great Filter: wreckage of space habitats would continue to reflect infrared long after berserkers cleanse all systems in the area)
Spectroscopy could prove the presence of interesting materials, but there might be a problem there… One of the best and most readily available structural materials is graphene. It is also excellent for radiating heat because it is pretty much perfectly black, absorbing a fraction of radiation of any wavelength equal to pi times the fine structure constant per each layer of carbon atoms ( https://arxiv.org/abs/2303.14549 ). Graphene is also very common in ordinary cosmic dust… perhaps not for the same reason. Though I don’t really understand the details, deeper IR emissions from graphene oxide have been suggested to cause ‘extended red emission’ ( https://arxiv.org/pdf/1908.07787 ).
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Markon May 18, 2024 at 12:57
Hi Paul
Great and informative article. I wondered what had happened to the search for Dyson artifacts, now I know.
Thanks…!
Regards
Mark
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Alex Tolleyon May 19, 2024 at 16:07
Mega engineering. I used to think it started with the Victorians – building bridges and large steel ships. However, it has a longer history. The Egyptian pyramids, the Biblical story of the Tower of Babel, The Roman roads connecting the empire (and Hadrian’s Wall), medieval castles, and cathedrals. In the 20th century, we were back to building the highest buildings, a throwback to Babel and the Florentine towers, with depictions of skyscraper cities in fact and fiction (Metropolis). Megaengineering seemed back in the exuberant 1960s with plans for a bridge spanning the Straits of Gibraltar, not to mention mega rockets (Saturn 5, N-1). With a brief “Small is Beautiful” (Schumacher) in the 1970s, we were back with exuberant mega engineering with the Burj Khalifa skyscraper in the UAE and now the planned mega city as a linear building in Saudi Arabia. I wonder if our Stone Age ancestors had similar ideas, as the later builders of Stonehenge and other megalithic structures.
Dyson’s “logical” ideas for maximal energy consumption seem more like the same. But as I have argued before, once complete, there is nowhere to go unless the same construction can be completed around neighboring stars. In which case they should be filling the galaxy as it doesn’t take more than a few millennia to complete to ensure energy growth matches economic growth (post-Malthusian, industrial [capitalist,] socio-political systems). Our current craze for cloud-based computing systems and now centralized AI are like the starting points for a planetary-scale need for huge energy-demanding computation systems, currently still small, but increasing energy demand in leaps and bounds and already causing problems in some areas with electrical and cooling water shortages. The problem with Dyson spheres is how to construct them as they need to be complete to fulfill their purpose. The swarms seem more sensible as they are useful from the first to the last independent component. Matrioshka brains seem even more fanciful as it seems that the civilization has to be hom*ogenous in its thinking to change a planetary system. I find that doubtful, just as we have difficulty in having hom*ogenous ideas on social and political systems. Such a civilization would have to be either like termite societies or permanent autocracies. Of course, my bias is showing in that I value Enlightenment ideas of individual freedom and democracy. We cannot assume that is the future for advanced civilizations.
We should not forget that the industrial period has been extant for a few hundred years, a mere eye-blink in time and that all of recorded human history is less than 15 millennia. This pales in time to our period as hom*o Sapiens, with increasing technological capabilities putting our civilization increasingly at risk from unforeseen catastrophes. Is spacefaring both a relief valve and a hedge for human civilization? Only after it has been achieved at scale. A Mars colony of even 1 million inhabitants would fail without the support of Earth. The path to civilizational longevity that allows [biological] ETIs to communicate may require keeping technology development controlled and economic growth restricted, a path that seems anathema to our species and current ideas.
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Alex Tolleyon May 19, 2024 at 16:24
Crazy idea. Apropos to the idea that we cannot see the universe as artificial.
To manage the longevity of a star, “star lifting” – reducing its mass to reduce its luminosity – is one mega engineering solution. The lowest useful mass may be greater than a brown dwarf, e.g. a M dwarf. What if the large fraction of stars being M_dwarf stars is not a natural phenomenon, but the result of engineering? The consequences would seem rather dire for biospheres, but maybe the civilization is no longer biological?
Another thought. If the Parenago Effect is real (see How to Explain Unusual Stellar Acceleration):
https://www.centauri-dreams.org/2021/08/20/how-to-explain-unusual-stellar-acceleration/
could this be the use of the star lifted material to drive these lower mass stars at higher velocities through the surrounding stars to increase the number of encounters? This would allow these advanced ETIs to reach new stars with their populations to repeat the process. Each star would most likely continue in its general direction of movement, but faster, and be aligned with an intercept of another star with a greater probability than expected by randomness. This last might even be a testable hypothesis with the Gaia data.
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Andrew Palfreymanon May 19, 2024 at 17:53
It feels very analogous to Victorians searching for signs of steam power.
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