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SETI: Are ‘Fermi Bubbles’ Detectable?

I’m enough of a perfectionist that when I get something wrong, I can’t rest easy until I figure out how and why I missed the story. Such a case occurred in an article I wrote for Aeon Magazine called Distant Ruins. The article covered the rise of so-called ‘Dysonian SETI,’ which is adding an entirely new dimension to current radio and optical methods by looking into observational evidence for advanced civilizations in our abundant astronomical data.

In the story, I homed in at one point on the work that Jason Wright and his colleagues Matthew Povich and Steinn Sigurðsson are doing with the Glimpsing Heat from Alien Technologies (G-HAT) project at Penn State. Keith Cooper went over the basics of this effort on Friday, putting his own spin on the group’s recent search of 100,000 galaxies. For more background, see Jason Wright’s Glimpsing Heat from Alien Technologies essay.

I noted in the Aeon article that the G-HAT team was examining infrared data from the Wide-field Infrared Survey Explorer (WISE) and the Spitzer Space Telescope in search of the signs of an advanced civilization. What I had wrong in my description was the statement that “Wright’s group is also looking for ‘Fermi bubbles’, patches of a galaxy that show higher infrared emissions than the rest, which could be a sign that a civilisation is gradually transforming a galaxy as it works its way across it.” I know I drew the idea of Fermi bubbles from Richard Carrigan’s work, and generalized from there, but generalizing was a mistake, because it turns out that the G-HAT team doesn’t believe Fermi bubbles are something we could detect.

Below is the ‘Whirlpool’ galaxy, M51, a beautiful image and a useful object for study because we are looking at a spiral galaxy in many ways like the Milky Way from an angle that lets us see it face-on. Could we see Fermi bubbles here?

m51center_hst

Image: The Whirlpool Galaxy is a classic spiral galaxy. At only 30 million light years distant and fully 60 thousand light years across, M51, also known as NGC 5194, is one of the brightest and most picturesque galaxies in the sky. The above image is a digital combination of a ground-based image from the 0.9-meter telescope at Kitt Peak National Observatory and a space-based image from the Hubble Space Telescope. Credit: N. Scoville (Caltech), T. Rector (U. Alaska, NOAO) et al., Hubble Heritage Team, NASA.

Richard Carrigan has studied this galaxy closely, looking for such Fermi bubbles, which he described in a 2010 paper. Here’s my description in Toward an Interstellar Archaeology, written for these pages in the same year:

Suppose a civilization somewhere in the cosmos is approaching Kardashev type III status. In other words, it is already capable of using all the power resources of its star (4*1026 W for a star like the Sun) and is on the way to exploiting the power of its galaxy (4*1037 W). Imagine it expanding out of its galactic niche, turning stars in its stellar neighborhood into a series of Dyson spheres. If we were to observe such activity in a distant galaxy, we would presumably detect a growing void in visible light from the area of the galaxy where this activity was happening, and an upturn in the infrared. Call it a ‘Fermi bubble.’

Carrigan (Fermi National Accelerator Laboratory) studied M51 and concluded that there were no unexplained ‘bubbles’ at the level of 5 percent of the galactic area. The Whirlpool galaxy seems like an ideal place to mount such a search given its orientation towards us. A Fermi bubble, if such things exist, might manifest itself as a void in the visible light we see in the image.

Carrigan talked about an expanding front of colonization as an advanced civilization moved through its galaxy, engulfing the galaxy on a time scale comparable to the galaxy’s rotation period or even less. But M51 produced no ‘bubbles,’ and James Annis would suggest that elliptical, rather than spiral, galaxies might be a better place to look for Fermi bubbles because ellipticals exhibit little structure, so that a potential void would stand out.

Here’s Carrigan in the 2010 paper (citation below) on how a civilization on its way to Kardashev Type III status might proceed:

If it was busily turning stars into Dyson spheres the civilization could create a “Fermi bubble” or void in the visible light from a patch of the galaxy with a corresponding upturn in the emission of infrared light. This bubble would grow following the lines of a suggestion attributed to Fermi that patient space travelers moving at 1/1000 to 1/100 of the speed of light could span a galaxy in one to ten million years. Here “Fermi bubble” is used rather than “Fermi void”, in part because the latter is also a term in solid state physics and also because such a region would only be a visible light void, not a matter void.

Wright and the G-HAT team are not persuaded by Carrigan’s Fermi bubbles. For one thing, as Carrigan has noted himself, bubble-like structures are not unusual in extragalactic astronomy, and spiral galaxies include areas that might mimic a void that would be hard to regard as anything but natural. In one of their recent papers, the G-HAT researchers add that with galactic arm widths on the order of ~ kpc, it is difficult to identify structures below this size scale.

The Annis idea, therefore, seems more useful, but for now let’s home in on that word ‘void.’ In the Aeon story, I referred to the galaxy VIRGOHI21 as a galaxy that contains a ‘void.’ But that’s a mistake, for as Jason Wright explained in a recent email, Virgo HI21 has no emissions at any wavelength except 21cm. It may, in fact, be a starless or ‘dark’ galaxy, a galaxy composed of dark matter, although the nature of the object is still controversial. The G-HAT team, according to Wright, has studied Virgo HI21 and found no infrared emission.

In any case, as Wright explained, the word ‘void’ isn’t appropriate, for galaxies do not actually contain them. Areas where there has been no star formation for the past 10 million years or so may manifest themselves as darker lanes between the spiral arms, and dust lanes may also appear dark, but Wright does not believe the shape of these darker lanes is consistent with the spread of a civilization. In any case, these are not voids. They contain just as many stars as other regions in the galaxy. So detecting Fermi bubbles gets to be more and more problematic.

Fermi bubbles would be hard to detect for other reasons as well, as explained by the G-HAT team and presented in their recent work. This is intriguing stuff, having to do with the time scales involved in the spread of a civilization and the motions of stars in that period — these ‘bubbles’ would not be static! I want to look at this issue next but probably won’t be able to get the piece written and published before Wednesday due to an intersection of competing duties elsewhere.

The Carrigan paper is “Starry Messages: Searching for Signatures of Interstellar Archaeology,” JBIS Vol. 63 (2010), p. 90 (preprint). The G-HAT paper I am discussing today and on Wednesday is Wright et al., “The Ĝ Infrared Search for Extraterrestrial Civilizations with Large Energy Supplies. I. Background and Justification,” The Astrophysical Journal Vol. 792, No. 1 (2014), p. 26 (abstract / preprint).

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  • Jason Wright May 11, 2015, 12:59

    Nice article.

    I’ll point out that the term “Fermi Bubble” is also taken – it refers to one of two regions of higher gamma ray emission discovered by the Fermi space telescope. They are apparently bubbles in the interstellar medium blown by activity at the center of the galaxy, but they are poorly understood.

  • Brian May 11, 2015, 14:19

    Yea, when I first heard the term I tried looking it up but only found the gamma rays, I think a new name is needed, maybe after who came up with the concept. This could actually complement our discussions on the last article very well, it doesn’t seem like anyone gets to KIII but everyone seems to think KII+ isn’t to unreasonable, 5% of the galaxy seems like more than enough for a stable civilization to use to survive any natural disaster without the effort of taking over the entire galaxy.

  • Marshall Eubanks May 11, 2015, 14:41

    If Virgo HI21 has 21 cm emissions, it has Hydrogen gas, so it can’t be pure dark matter.

  • Marshall Eubanks May 11, 2015, 15:25

    Call them Dyson Bubbles

    – that name isn’t taken and
    – it is really about the notion of a region dominated by Dyson sphere, which Fermi had nothing to do with.

  • Keith Cooper May 11, 2015, 18:16

    If the estimations of Tipler, Crawford etc are correct, then another factor to consider is that it would only take a few million years to colonise a galaxy. When we consider that galaxies are 12-13 billion years old, that’s a tiny fraction of their lifetime, so the chances of catching a galaxy in the middle of the process of being colonised might be very slim. In that case we’ll either find galaxies fully colonised, or not at all, rather than in the transitional phase of mid-colonisation. Of course, the chance of finding a galaxy in such a state increases the longer it takes to colonise a galaxy and build all those Dyson spheres.

  • James Stilwell May 11, 2015, 19:19

    It’s still curious how sighting evidence of a civilization 30 million light years distant and thus 30 million years old is going to affect the mind of the observer…I’d wonder–did they survive the ages? I’d rather come upon Clarke’s Monolith on the moon a decade from now…If aliens were on the Moon, they were on the earth too…
    But it’s moving to imagine M-51 people…
    If they traveled from star to star, we will too…

  • Brian May 11, 2015, 20:17

    Dyson bubble is good, Kardashev bubble might be good too since it would be an observation of his ideas.

  • Eniac May 12, 2015, 0:16

    As Paul hints at, a galaxy is not a static medium where bubbles would have time to develop. Such bubbles would be sheared into streamers in relatively short order. The spread of civilization would look more like milk stirred into coffee than a clearly delineated expanding bubble.

  • Zanstel May 12, 2015, 6:41

    Probably the idea of “advancement” through exponential energy use is bogus.

  • Harry R Ray May 12, 2015, 9:47

    This is SLIGHTLY off topic, but Astro-Ph has an abstract today of a very peculiar white dwarf: PG 0010+280. Temperature: 27280K, 16 Megayears , Excess at 3-8 $/mu$m (BUT: Relatively LOW emmission AT 8). MOST IMPORTANT: NON-DETECTION OF HEAVY ELEMENTS in its atmosphere. The authors say that this is the youngest and hottest white dwarf with the above mentiones infrared excess ever detected? They give two POSSIBLE explanations: ONE an opaque disk within the tidal radius of the white dwarf, or TWO: a 1300K blackbody. One possibility for thid blackbody would be a “Hot Jupiter”, the other an old brown dwarf whose heat emmission would be as a result of radiation from the white dwarf. To me, the disk scenario seems unlikeky, due to the apparent lack of pollutants in the atmosphere. A brown dwarf (and MAYBE a giant planet should be detectable via radial velocity. SHOULD THIS NOT OCCUR, could a Dyson SPHERE (or shell be a viable ALTERNATIVE explanation. If anyone who sees this comment today could go to http://www.arxive.com and click on Astro-Ph and read the paper, I would appreciate your input!

  • Francisco May 12, 2015, 9:49

    What Zanstel said. I mean for example, isn’t the human population supposed to balance itself out around 10 billion individuals later in this century? And not all planets will have the same capacity to sustain the amount of people as Earth does. I would also argue the notion that the more a society advances, the less energy it uses (as it becomes more efficient, self generation in nuclear reactors, etc).

  • John May 12, 2015, 10:34

    AM I right in thinking that stars keep their orbital distance from the gaslctic centre much more consistently than their exact oriention to eachother? If so you’d see a dark smear, followed by a dark lane/ring.

    If such a power hungry civilisation exists I imagine that there’d be other signs of galctic scale engineering, with dyson style power collection being only poart o the civisations efforts. Who’d build a city of power stations with no houses or shops?

  • Marshall Eubanks May 12, 2015, 13:06

    John, on a “short” term (say a few galactic rotations) the Sun undergoes a number of “epicycle” type motions, one in and out of the galactic plane, and one in the plane. The galactic potential is not Keplerian, so these have different periods – here are some pictures http://www.astro.umd.edu/~cychen/MATLAB/ASTR320/Spring2011/galorbs.html

    Yes, the Sun and other local stars will wander away from each other at roughly 30 km / sec (or 10^-4 c), so after a billion years or so, our neighbors today will be spread throughout the galaxy. Even though our motion (and most of the our neighbors) is nearly a circular orbit there is even evidence that over multiple billions of years a star such as the Sun might wander considerably radially (we might have been closer to the galactic center a few billion years ago).

    All of this means that a “Dyson bubble” will not stay a bubble for long, at least on galactic time scales.

  • Alex Tolley May 12, 2015, 13:48

    @Francisco What Zanstel said. I mean for example, isn’t the human population supposed to balance itself out around 10 billion individuals later in this century?

    On Earth, yes. But if we move off planet, the solar system could support orders more population based on asteroid and Oort resources, although we will still be limited by important biological element5s such as phosphorus.

    I would also argue the notion that the more a society advances, the less energy it uses

    So far that is not teh case. We are getting more energy efficient, but total energy per capita is rising. Even with high energy efficiency, we would end up with some minimal energy per capita use. We could reduce it by letting go of out technology, but then the population that is supportable on Earth may dwindle to the millions.

  • Alex Tolley May 12, 2015, 13:53

    @Eniac The spread of civilization would look more like milk stirred into coffee than a clearly delineated expanding bubble.

    That may be harder to detect, but I would have thought that such patterns would be detectable as statistically non-random if the galaxy can be imaged with sufficient resolution. Maybe a good case for humans to look at in a crowd manner, rather than a machine.

  • Alex Tolley May 12, 2015, 14:15

    @Keith Cooper
    If the estimations of Tipler, Crawford etc are correct, then another factor to consider is that it would only take a few million years to colonise a galaxy. When we consider that galaxies are 12-13 billion years old, that’s a tiny fraction of their lifetime, so the chances of catching a galaxy in the middle of the process of being colonised might be very slim. In that case we’ll either find galaxies fully colonised, or not at all, rather than in the transitional phase of mid-colonisation.

    The assumption behind this is that once a star is colonized, it remains colonized. But what if that isn’t the case and stars only temporar4ily hold a local civ, which then fades and later re-emerges. The stars in the galaxy might blink on and off with high technology cultures like Conway’s “Game of Life”. That might be hard to detect using observational methods.

  • Mark Zambelli May 12, 2015, 14:33

    @James Stilwell
    I, for one, hold the question of “are we alone” as one of the most important questions of all. To have it definatively answered that the Universe can perform not only the ‘trick of life’, but of intelligence, more than once would be wonderful.

    @John
    I’m thinking similarly. Assuming Dyson Sphere building isn’t the way to go, would a KIII-ish civ (with or without an energy abundance) still give itself away in the IR thanks to all their other, non-Sphere related, technology?, all-the-while leaving their galaxy’s starlight (relatively?) untouched.

    I’ll also second Keith Cooper when he says that, given the timescales at play, if (I hope ‘when’) we detect anything, it’ll be a galaxy-wide phenomena… the chances of catching anyone undergoing the processes of expansion is exceedingly slim, especially as now we have the recent 100,000 galaxy survey to give us some bound in the potential sample size. If only it was anywhere near as easy as finding all those locally-rare extra-galactic supernovae.

  • Jimbot May 12, 2015, 14:44

    Sorry to spoil the party for all you astrophysics buffs, but along the lines of Zanstel’s comment, have you heard about atmospheric CO2 ,CH4 and a few other deadly gases? Noticed anything peculiar in the reports from the Arctic these days?

    http://arctic-news.blogspot.ca/

    It seems patently obvious that we ain’t goin’ anywhere, unless some good guy ETs show up real soon.

  • Mark Zambelli May 12, 2015, 15:21

    @Alex Tolley

    I love your ‘Game of life’ analogy… I admit I hadn’t considered that scenario and if a Myr expansion did unfold that way then we’d need hi-rez imaging to spot those Dyson-bubbles in those dotted configurations. I wonder if the civ would dismantle their Dyson Spheres and if not, how stable they would be over time if unattended and after the lifetime of the autonomous AI that regulates things? If they’re still there then no problem.

  • Keith Cooper May 12, 2015, 16:16

    @Alex Tolley

    If one civilisation dies off, its neighbours may well just jump straight in and replace them, depending on how far away they are. In a largely populated galaxy we might expect extinct civilisations to be replaced rather quickly, so there might not be blinking on and off effect, or if there is it might be shortlived. Also, Dyson spheres may well be able to far outlast their builders anyway. They wouldn’t necessarily switch off when their builders die off.

    @Jimbot

    To me the mark of an intelligent civilisation is one that can work through its problems. I have faith that humanity can do that and emerge on the other side. And Dysonian SETI might not be as far removed from fixing the climate as at first appears. First there’s Carl Sagan’s point that if we discover an advanced extraterrestrial civilisation it will prove that it is possible to surpass our problems and live long into the future. Besides that though, the technology we refer to when discussing Dysonian SETI is essentially a swarm of solar collectors generating energy. If we can move much of our industry off Earth and into orbit, generating energy from our own solar collectors – we just need a handful in near-Earth orbit – we can start to help solve the problem of climate change at the root of the cause, which is carbon emissions from industry. Jason Wright points out that we’re already beginning to build a the essence of a Dyson sphere, just by putting solar panels on the space station. Maybe all Dyson spheres start of as small scale. The asteroid mining companies want to build solar energy collectors from the material they mine, and then just beam that energy back down to Earth as microwaves. It might take several decades – and granted we need to hurry up if we’re going to start fixing the climate – but it is feasible.

  • Rob Henry May 12, 2015, 17:22

    Yes Jimbot, a problem with human civilisation is its over-reliance on a form of science, which demands that repeatably observed phenomena are the only ones that exist until denial can no longer be maintained. This is seen in such logical fallacies as that ‘extraordinary claims require extraordinary evidence’, when logic says all prediction that succeed at a certain confidence level are equally valid, the unexpected ones doing so demanding MORE followup attention, not less.

    This does not solve the problem here though, as it seems unlikely that many ETIs would share this most peculiar flaw. For those others, logistic growth towards a Dyson swarm would present no problems, save for growth likely being at a slower pace.

  • Eniac May 13, 2015, 0:10

    Rob Henry: You apparently misunderstand the “extraordinary claims” logic. It is not a fallacy, rather it is solidly based on the statistics of multiple comparisons and reporting bias. Proof of extraordinary claims will be attempted more often than that of routine claims, increasing the expected number of false positives (aka type II error). In addition, extraordinary false positives are more likely to be widely reported than ordinary ones, further exacerbating the problem.

  • Alex Tolley May 13, 2015, 1:36

    @Keith Cooper

    If one civilisation dies off, its neighbours may well just jump straight in and replace them, depending on how far away they are. In a largely populated galaxy we might expect extinct civilisations to be replaced rather quickly, so there might not be blinking on and off effect, or if there is it might be shortlived.

    I don’t mean to shoot down your model. Just offer an alternative one.

    Also, Dyson spheres may well be able to far outlast their builders anyway. They wouldn’t necessarily switch off when their builders die off.

    Given how hard it is to construct a true sphere, we really expect a swarm instead. These may be standalone units, or more likely powering space habitats. Whether these habitats remain stable and “empty” is one option. They may decay over time just like terrestrial structures, or even be cannibalized as Roman buildings were in Britain after Rome left.

    I just want to present alternatives to the standard thinking about KIIIs stably filling a galaxy without dying. As I said earlier, once a galaxy is filled, growth stops, so the KIII civ becomes static in this regard. A model that allows for dynamic growth and decay allows for long term local regrowth after a setback. Those setbacks may even be due to war, other destructive events or even uncontrollable natural events that either destroy local cultures or force migrations.

  • J. Jason Wentworth May 13, 2015, 3:11

    “Fermi bubbles…” (Didn’t Don Ho write that song? :-) ) Seriously, regarding the expected infrared signatures from them, might they vary considerably, depending on the raw materials that are available in each given planetary or stellar system? As has been recently discovered, some exoplanetary systems are deficient in metals, yet are rich in “Alpha Elements” (carbon, oxygen, etc.–I forget the other ones). Depending on what the astro-engineers have available to build the bubbles from, it would seem that they might be more–or perhaps less–translucent (or opaque) to infrared radiation.

  • Keith Cooper May 13, 2015, 9:40

    @ Alex,

    No worries, models are there to be shot down, so fire away!

    It strikes me though that we’re assuming that every Dyson sphere/swarm gets finished. I ‘m not sure what the timescales of building a complete swarm are, but I imagine the timescales are large enough for societies to collapse, for motivations or politics to change, for wars to occur. Maybe half way through they decide we’ve got enough energy thanks, and leave it at that. Any number of things could interrupt with the construction of a Dyson sphere. – maybe there’s a universe of half-built Dyson spheres out there and we’d expect a much smaller infrared excess from galaxies in that case.

  • ljk May 13, 2015, 12:45

    How well could we detect a Ringworld? And no I don’t care if the MIT nerds chanting outside that 1971 science fiction convention said it was unstable. If you can build such a thing you will figure out how to make it stable in the first place, or you wouldn’t do it at all. There has to be SOME logic in the Universe, unless all creatures are inherently mad.

    http://io9.com/5524851/if-aliens-have-built-dyson-spheres-or-ringworlds-nearby-how-would-we-detect-them

    http://www.universetoday.com/102348/hunting-for-alien-megastructures/

    http://sites.psu.edu/astrowright/2013/03/09/artifact-seti/

  • James Stilwell May 13, 2015, 16:17

    So the galaxy becomes a soup of many civilizations…
    Sounds sensible and likely at sub light speeds…
    One civilization discovers another and war erupts…
    The Territorial Imperative being God’s plan…
    You know the drill, people…Empires rise…
    Who does the counting and who gets counted?
    The Artilects are the immortals in this game…
    Flesh will not survive even for 50,000 years…
    Unless someone invents faster than light travel…

  • Rob Henry May 13, 2015, 16:37

    ENIAC writes “You apparently misunderstand the “extraordinary claims” logic. It is not a fallacy, rather it is solidly based on the statistics of multiple comparisons and reporting bias.”

    Yes ENIAC, that’s how such a methodology should be employed, and yes it is employed correctly on the odd occasion. And finally yes that rare exception is how they justify this fault to themselves.

    The first time I noticed this fault I was a kid in school and the life tests for the Viking missions were returning their data. All three of them tested positive for life by prior accepted criteria, but the consensus was their were other conceivable explanations Even though from that day to this, no known mineral-chemical combination could replicate those results (even after an extensive search) few scientists ever deemed a follow up necessary.

    That is the way its always done such that it takes us an age to notice that we might one day be facing a potential mortal danger such as anthropogenic global warming. That is a very dangerous methodology.

  • Eniac May 13, 2015, 23:52

    Alex Tolley:

    The assumption behind this is that once a star is colonized, it remains colonized.

    I do not think this is true. A much weaker assumption is sufficient: Colonizations happens more often than extinction (including re-colonization, of course). This is almost the same as assuming colonization happens, period.

  • Rajsun May 14, 2015, 5:31

    On the subject of blue stragglers in the aforementioned article ‘Distant Ruin’ you wrote for Aeon Magazine, you postulated that these anomalous stars could be signposts of advanced alien civilizations at work i.e.

    Quote: “Beech thinks blue stragglers could mark a Kardashev Type II culture trying to preserve its habitat.”

    I agree that these blue stragglers do look kinda incongruous and are probably worth another look but wouldn’t yellow or orange or even red stragglers (no idea if they exist or are expected/suspected to exist) equivalent to these blue oddballs be even more promising targets at least from our standpoint (albeit a prejudiced one)?

  • Paul Gilster May 14, 2015, 8:50

    Rajsun, I’m not familiar with yellow, orange or red ‘stragglers,’ but the blue stragglers really catch the eye because they show up in places where we would expect predominately older stars. Thus Beech’s idea that these could be older stars that a KII culture has reinvigorated by pumping hydrogen back into the core. As far as I know, these are the only stragglers; i.e., stars fitting this oddball description.

  • ljk May 14, 2015, 9:31

    Just to play devil’s advocate, a natural possibility for blue stragglers:

    http://www.mso.anu.edu.au/~jerjen/researchprojects/bluestraggler/bluestraggler.html

    To quote:

    “Blue straggler stars appear to violate standard theories of stellar evolution, in which all stars born at the same time should lie on a clearly defined curve in the Hertzsprung-Russell diagram, with their positions on that curve determined solely by their initial mass. Since blue stragglers often lie well off this curve, they may undergo abnormal stellar evolution.

    “The cause of this is not yet clearly known, but the leading hypothesis is that they are current or former binary stars that are in the process of merging or have already done so. The merger of two stars would create a single star with larger mass, making it hotter and more luminous than stars of a similar age. If this theory is correct, then blue stragglers would no longer cause a problem for stellar evolution theory; the resulting star would have more hydrogen in its core making it behave like a much younger star. There is evidence in favor of this view, notably that blue straggler stars appear to be much more common in dense regions of clusters, especially in the cores of globular clusters. Since there are more stars per unit volume, collisions and close-encounters are far more likely in clusters than among field stars.

    “One way to test this hypothesis is to study the pulsations of variable blue straggler stars. Blue stragglers rapidly rotate at a rate of 75 times that of the Sun’s rotation. They appear to be two to three times the mass of the other cluster stars present. The most recent research reveals that near-by stars to blue stragglers have significantly less carbon and oxygen than their neighbors. This suggested that one star becomes hotter and bluer by pulling material from an orbiting star. The star thatÕs had material stolen from it has deep regions exposed that show areas where the starÕs original carbon had fused into heavier elements.”

    They may also be due to stellar mergers, which makes sense in a cluster:

    http://blogs.scientificamerican.com/basic-space/blue-stragglers-formed-by-engulfing-red-giants/

  • ljk May 14, 2015, 9:32

    A Centauri Dreams article on blue stragglers from 2011 here:

    https://www.centauri-dreams.org/?p=18173

  • ljk May 14, 2015, 9:33

    SolStation is another excellent source for stellar information:

    http://www.solstation.com/x-objects/bluestrag.htm

  • Mark Zambelli May 14, 2015, 11:30

    Given we’ve raised the point about the longevity of unattended Dysonian structures, I’m wondering what kind of heat signatures might be produced, and whether we could ever hope to discern if it was unnatural, when an abandoned Dyson Sphere is destroyed…ie, the collectors lose station-keeping etc, and collide. I would imagine this will proceed as a cascade in a swarm that is dense enough (several million/billion collecters).

    The debris surrounding the star as a result would heat up and emit an IR excess. With our ability to study proto-planetary discs and even to deduce extrasolar-comet populations or asteroid collisions in nearby systems, would the destructive scenario above mimic natural emissions or could we tease-out any signs it was caused artificially?

  • ljk May 14, 2015, 13:38

    Why would a Dyson Shell be unattended? Do you mean by organics? Have you seen Robert Bradbury’s papers on Matroishka Brains? Dyson Shells would BE the dominant life form, as he said.

    http://web.archive.org/web/20090223093348/http://aeiveos.com:8080/~bradbury/MatrioshkaBrains/index.html

  • Jimbot May 14, 2015, 15:14

    @ Keith Cooper

    “To me the mark of an intelligent civilisation is one that can work through its problems.”

    Hi Keith, thanks for your reply. I’m of the view that we have more of an unsolvable dilemma leading to our certain demise rather than a problem. Anyway, this discussion you all have going here is interesting
    nonetheless.

    @ Rob Henry

    “This does not solve the problem here though, as it seems unlikely that many ETIs would share this most peculiar flaw.”

    I agree, Carl Sagan’s remark referred to by Keith is implying ETIs were once like us, but this seems like an unwarranted assumption. In my view the only way we are likely to get through the next fifty years or less will be with the help of some such beings, that never had our defective civilisation.

  • Marshall Eubanks May 14, 2015, 22:24

    @ljk “How well could we detect a Ringworld? ”

    We could detect a Ringworld (and, what I regard as a more practical habitat, a
    “Culture” Orbital) through gravitational lensing. Consider an orbital (which would have mass in orbit about a star, not centered on a star) that is perpendicular to the line of sight. For raypaths that pass _outside_ of the ring, the mass of the ring will appear to be a spherical mass, much like the lensing from a planet. However, the photons that pass _through_ the ring will not be lensed by it, the ring lensing being canceled by equal and opposite perturbations from opposite sides of the ring. This jump back to an unlensed state (and then a jump back to lensing at the other edge of the ring) would be very easy to detect given suitably dense observations, should a lens source (the distant background star) actually pass directly behind the orbital. A ringworld would have a similar lensing effect, but since it has a star in its center, the total effect would appear as a step function change in the star’s lensing as the source passed behind the ring; in principle observable, but in practice probably harder to distinguish from other, more natural, distributions of mass.

  • Mark Zambelli May 15, 2015, 9:34

    @ljk

    “Why would a Dyson Shell be unattended? Do you mean by organics? Have you seen Robert Bradbury’s papers on Matroishka Brains? Dyson Shells would BE the dominant life form, as he said.”

    I’m trying to imagine a scenario whereby the Dyson swarm builders fall by the wayside and their AI control systems breakdown before the system can be re-colonized. Alex and Keith have made good counter points in this discussion referring to how long any system will remain colonized so the senario I brought up seemed a logical extension of any interim time.

    Either the system is stable and under no threat (colonized) or the system is abandoned and then subsequently re-colonized. If the re-colonizing takes a lot longer in some systems than others, and in those small subset some non-organic caretakers breakdown, then this ‘may’ lead to the ‘unattended failure’ scenario I mentioned.

    I like Matrioshka Brains (and I have, maybe once too often, referred to Charles Stross’ ‘Accelerondo’ which relies heavily on that idea as a plot device) and I know exactly where you’re coming from. However, even if all the Dyson Spheres were supporting non-biological civs, it’s the small subset that somehow go extinct that I was particularly musing over. If the Matrioshka Brains/Dyson Spheres are all immortal in every single instance then the part of the discussion about civs going extinct and then re-colonizing these systems is rendered moot and we’re back to the simpler concept of a KIII galaxy being observed to be completely transformed with no gaps around any star systems.

    I just wondered what a failed Dyson Sphere of orbital collecters would do over time and whether we could tell, even in principle.

  • Mark Zambelli May 15, 2015, 9:36

    @ljk
    Oh, my manners… thankyou for the link BTW :)

  • ljk May 15, 2015, 16:57

    You are welcome, Mark Zambelli. Here is another source of information on Dyson Shells/Swarms you and others may find useful, or at least entertaining:

    http://www.orionsarm.com/eg-article/4845fbe091a18

    Scroll all the way down to the Related Articles section for links to even more info on Dyson Shells.

    While I am not saying that a Dyson Shell could not fail, if the Brain kind (there is also a smaller type labeled Jupiter – guess how big it is?) has many “brains” I do not see how they could all fail at once or even over time, as there would be so many backups and I will presume they were not designed to be like the alien warriors in the first Avengers film, to all collapse if the main command is destroyed. And there would have to be many brains as the very nature of the Dyson Shell is to be very large to collect all that solar energy. I am also presuming the connections et al do not function at FTL speeds.

    If you accept the possibility of a M/J Brain, the next question is what is so major and complex to study and comprehend that such a huge artilect would be required for the job? Well… the observable Universe is 13.7 billion years old, is 90 billion light years across, and contains 100 billion galaxies with hundreds of billions of stars each and even more planets and other bodies circling them – all the way down to the quantum level where existence is very different from the macroworld. Then you have all these possible life forms and then throw the possibility of an infinity of alternate universes into the mix and wheh!

    One indeed might need a lot of processing power and energy to solve such riddles, if I understand my highly advanced, futuristic alien technology correctly. And figuring out the answers to Life, the Universe, and Everything may just be the tip of the cosmic iceberg.

  • Eniac May 16, 2015, 23:25

    I do not think Matrioshka Brains will be built for the purpose of studying something in particular, much less Life, the Universe, and Everything. Rather, computing hardware will be the equivalent of real estate, a place to live for electronic minds. Some may study interesting problems, but most will probably spend their allotted CPU cycles watching the equivalent of TV show reruns or playing the equivalent of video games. I doubt that this aspect of culture will change much….

  • Marshall Eubanks May 18, 2015, 5:50

    Note that Matroishka Brains might or might not be detectable by GHAT type surveys – that depends critically on the temperature they want to run at. If they are made of silicon or germanium, and run at supercold temperatures, then a Matroishka Brain Dyson sphere might have a temperature of only a few degrees above the CMB, and thus would be hard to distinguish from the background. Conversely, they might be made of quark matter (much denser, thus leading to much faster computations for the same mass) and then might run very hot (say, up at the keV level). In that case, the Dyson sphere might be inside the star, down near the core; again, not detectable by a IR survey.

    I thus think that the GHAT surveys say something about the prevalence of Dyson’s original “agricultural” Dyson spheres, but not much about the prevalance of Matroishka Brains.

  • Mark Zambelli May 18, 2015, 6:10

    So, is the natural endpoint for any Dyson Shell of collectors a Matrioshka Brain inhabitted by non-organics / transcended post-civs? If so, then they may well become immortal at that point… they’re radiation-hardened by design, occupy systems cleared of debris / former-resources, and have simply staggering intellects; a portion of which would surely be allocated to the problems of ongoing longevity, with even a miniscule portion of said thinking-power being orders of magnitude greater than even our visions of a super-intelligence.

    Or will some (most? a few?) Dyson Shells halt somewhere on this curve, maybe when cpu-cycles become so cheap and plentiful there isn’t a strong drive to develop further to the endpoint of becoming a full blown MB? Will a happy balance between the benefits gained, over wanting more, be met well before then. Perhaps in the early stages of developing Dyson Shells those civs are already godlike and have more than enough resources to mount colonization programs so spread out rather than stay in one place pushing for the MB ideal? But then again, would there ever be an “enough is enough” mentality?

  • ljk May 18, 2015, 8:45

    Yes, just as we really sent humans to the Moon for geopolitical reasons over lunar science, if Dyson Shells are built they may be done for reasons other than expanding knowledge (condos for Artilects?). In that vein here is another possible reason for their existence:

    http://www.orionsarm.com/eg-article/48fe49fe47202

    All that being said, this is still good for SETI in terms of finding Dyson Shells /Type 2 and 3 civilizations as they may still exist, even if not for the noble scientific reasons so many SETI practitioners would like to think.

    Personally I never really bought into aliens beaming the equivalent of the Encyclopedia Galactica across the Milky Way to altruistically enlighten all who can detect the broadcasts. Perhaps I have just been stuck among the one selfish, warlike species in the Universe that does not share or play well with others unless there is a benefit to itself, but that is one thing SETI is supposed to learn about our neighbors, right?

  • ljk May 18, 2015, 10:48

    Maybe the future for all smart beings is to become less smart, which is why our mostly token SETI efforts cannot find them:

    http://articles.latimes.com/1985-10-23/news/vw-14060_1_brains

    “Years ago my mother used to say to me, she’d say, “In this world, Elwood, you must be” – she always called me Elwood – “In this world, Elwood, you must be oh so smart or oh so pleasant.” Well, for years I was smart. I recommend pleasant. You may quote me.”

    – Elwood P. Dowd (Jimmy Stewart) in Harvey (1950)

    https://www.youtube.com/watch?v=EzOIhLJ1C-Y

  • Eniac May 18, 2015, 21:46

    Will a happy balance between the benefits gained, over wanting more, be met well before then.

    I would think that there will always be pressure to fill any available CPU cycle with more and greater minds, particularly if these minds are computational and thus easily upgraded and duplicated. This will necessarily translate into demand for more hardware and energy.

    What limit would there be other than the availability of resources?

  • Mark Zambelli May 19, 2015, 11:25

    Eniac,
    Well, in an über-enlightened civ much further along than us, I would hope that a self-imposed limit on available resources might be in their mindset. Cramming more and more sentient beings into available substrates because you can and then feeling pressure to expand, seems very human-20th Century. This kind of mentality has kinda been the main problem with our own thinking and has driven us to where we are today… possibly this is a great-filter for civs.

    Yet the Dyson-builders may likely have had to get past their own filters to become capable to expand so the view of available resource-use and its implications may be very different… maybe a more sedate growth levelling off to some stable plateau after some length of time. Stable but not stagnent, with incremental changes in efficiency and re-design / re-allocation to allow for growth without expansion of the Dyson Shell architecture.

    My head hurts trying to think of motivations for post-civ activities; mainly because it is impossible for any of us to predict. What new tech will they employ that renders our discussion of cpu-cycles moot, for example? If something like Iain M Banks’ “Minds” could exist (advanced processors occupying gigantic volumes in a higher dimension yet enclosed in a two-metre ellipsoid… roughly), would tech like that negate the need for expanding your Shell any further? What of all the other ‘magic’ they’ll develop once that early-stage Dyson Shell snowballs in its use of cpu MIPS?

    I don’t disagree with your observations about expanding to use available energy as you stated above, Eniac, I’m just imagining there may be a few points along the curve from fledgling Dyson Shell to MB where a civ could ‘step-off’, so-to-speak. After all, Shells should be easier to find than a MB emitting waste heat a fraction of a K above the CMB radiation?

  • Eniac May 19, 2015, 23:29

    Mark:

    Cramming more and more sentient beings into available substrates because you can and then feeling pressure to expand, seems very human-20th Century. This kind of mentality has kinda been the main problem with our own thinking and has driven us to where we are today

    I would argue that this mindset far predates the 20th century and is hardly restricted to humans. That indeed there never was a time where life of any kind did not try to “cram and expand”. As you say, this could be different in future advanced technological civilization, but it would be novel and I am not holding my breath.

    I would also argue that “where we are today” isn’t all that bad, that it is in fact a lot better than where we have ever been before. From this it kinda, sorta follows that maybe the mindset is not as much of a problem as you appear to presuppose.

  • Marshall Eubanks May 21, 2015, 2:26

    Note that the mostly technologically advanced human cultures are not fully reproducing themselves (or, if they are, it is because they are allowing immigration from other, less technologically advanced cultures). I would thus conclude that our civilization is passing beyond “cram and expand” even in our own time.