“Were the chemicals here on Earth at the time when life began unique to us? We used to think so. But the most recent evidence is different. Within the last few years there have been found in the interstellar spaces the spectral traces of molecules which we never thought could be formed out in those frigid regions: hydrogen cyanide, cyano acetylene, formaldehyde. These are molecules which we had not supposed to exist elsewhere than on Earth. It may turn out that life had more varied beginnings and has more varied forms. And it does not at all follow that the evolutionary path which life (if we discover it) took elsewhere must resemble ours. It does not even follow that we shall recognise it as life — or that it will recognise us.”
— Jacob Bronowski, from The Ascent of Man
How accurate do you think we are in projecting what extraterrestrial civilizations might do? The question is prompted by recent speculation on Dyson spheres and the supposition that advanced cultures will invariably build them. After all, a Dyson sphere would seem to be a natural for beings who wanted to extract as much usable power as possible from their sun. Such a civilization, which Nikolai Kardashev thought of as ‘Type II,’ using all the power of its star, would doubtless think breaking up a local gas giant and using it to enclose that star made sense.
So let’s assume for a moment that extraterrestrial beings follow a game plan we humans have devised. And let’s take it to the next logical level. Going from Type II to Kardashev’s Type III, cultures that exploit the resources of entire galaxies, we would have to admit the possibility of creating Dyson spheres around every star in a galaxy, an interesting thought when you ask what methods are best for detecting signs of intelligent life elsewhere in the universe.
Image: A Dyson sphere allows a civilization to exploit maximal energy from its star. Excess infrared could conceivably mark its location to SETI-oriented astronomers. Credit: Guillermo A. Lemarchand.
Hunting for Dyson Spheres
For instead of listening for radio broadcasts or looking for optical beacons, finding Dyson spheres, either by themselves or in a wavefront spreading through a galaxy, is an observational SETI that could be successful even if its targets have no interest in trying to contact us. Thus Bruce Dorminey’s recent essay on SETI’s new wave, the idea of searching for distinctive signatures of Dyson spheres and their derivatives. Dorminey, author of the fine Distant Wanderers: The Search for Planets Beyond the Solar System (2001), tracked down people who have begun looking for such objects. People like Dan Wertheimer (UC-Berkeley), who analyzed a thousand solar-type stars (having culled those at least a billion years old), looking for excess infrared. 32 stars made the final cut and were examined for radio or optical transmissions, with no sign of alien intelligence.
Dick Carrigan (retired from Fermilab) has spent five years on 11,124 sources identified by the Infrared Astronomical Satellite (IRAS). It’s all in Dorminey’s essay, how Carrigan went after objects with an infrared temperature of 200-600 K, looking for the radiation of waste heat, again finding no signs of intelligent activity when scanning several contenders for anomalous radio signals. Or consider James Annis (Fermilab), who analyzes not single stars but entire galaxies looking for signs of engineering.
Here’s Annis on the possibilities, looking for a galaxy that might emit only 100th of one percent of the light expected from it, the possible signature of astroengineering at work:
“If you were to see obvious dust clouds around a candidate galaxy in the infrared, then it could be a dusty starburst galaxy where the dust is very clumpy and you can see ongoing star formation. But if you got an infrared galactic image that was completely smooth with no lumpiness, that’s an interesting object.”
Dorminey notes that to achieve this level of dimming on a galactic scale, a Type III civilization would need to have gone to work on just about every star in its galaxy. Which cannot, of course, be ruled out when you’re dealing with technologies at this level. Even here, though, we have to avoid being too doctrinaire. One argument against intelligent life in the nearby cosmos is the lack of Type III engineering, the assumption being that any culture that could harness an entire galaxy’s power would already be blindingly obvious to us. “My guess,” says Dan Wertheimer, “is that just from the astronomical data on file we would have discovered such a civilization by accident.”
Alien Technologies, Human Assumptions
Would we? That would bring us back to Type II as the only kind of advanced civilization to look for, but I disagree with Wertheimer. Here’s one reason why: In trying to understand hypothetical alien cultures, we’re assuming we can extrapolate forward from our own technology to what we would do if we had the necessary tools. Thus Dyson’s sphere, maybe 150 million kilometers in radius, a meters-thick shell rotating around its star. We can see this as a desirable outcome, so we assume aliens would as well. But would they? Perhaps a Type II society would have made breakthroughs in energy management that would render a Dyson sphere a historical curiosity, like some early 19th Century idea of a flying machine powered by flapping wings and a steam engine.
No, I can’t imagine what those breakthroughs would be, but then, that’s the point. How accurate can we be about predicting what science will find down the road? As Brian Wang has recently noted, projecting technology on our own planet out even fifty to a hundred years is all but impossible. For that matter, how can we be sure advanced engineering works would even be detectable, much less understood? My border collies are supremely intelligent dogs (one of them, anyway), but do they understand the difference between artifact and natural object? Do they know what a technology is? Yet the gap between border collie and human could be minor compared to the gap between human and extraterrestrial, especially if the latter has been developing its own technology for millions of years, if not billions.
None of which is to downplay what Wertheimer, Carrigan and Annis have done. Although the odds are daunting, I’m all for keeping our eyes open, and if a search for anomalous stars with excess infrared emission turns up interesting objects, let’s by all means investigate them. If we find galaxies with high infrared and low optical luminosity, let’s subject them to detailed scrutiny. But let’s not make any more assumptions than we have to. A negative result in a search for Dyson spheres or anomalous galaxies may only point to the limitations of our ability to project where technologies go as societies enter higher Kardashev levels.
Anomalous Galaxies and Their Uses
If you want to find something anomalous about galaxies, consider the case of NGC 5907, a spiral galaxy 39 million light years away. Observations of this galaxy in 1998 by Michael Liu (UC-Berkeley) and an international team of astronomers showed an odd mix of stars. Expecting to see hundreds of bright stars in their field of view, the researchers found only a few. Evidently twenty times more light comes from dwarfs than giant stars in the halo of this galaxy. Liu, lead author of the paper on this work, described the finding this way:
“Our results force us to turn to more esoteric descriptions of the stellar content of NGC 5907’s halo. In particular, our data combined with the measured colors of the halo suggest a very metal-poor stellar population with an enormous excess of faint dwarfs. This is the first direct evidence of a substantial population of stars which is essentially all dwarf stars. Such a population has been invoked in the past as a constituent of the dark matter making up galaxy halos.”
Image: NGC 5907. Can an entire galaxy become the subject of advanced engineering? If so, would we recognize the result? Credit: Brad Ehrhorn, Dan Azari, and Chris Lasley/Kitt Peak Advanced Observing Program.
Larry Klaes recently noted this as an example of anomalies that could be related to engineering on the galactic scale. His point was not that NGC 5907 demonstrates such, but that given the vast number of galaxies we have to observe, our attempts to examine them in the context of SETI are in their infancy. And if I am right that a Type III civilization is going to be extremely difficult to recognize, then hunting for galactic anomalies makes sense in the context of a broader search, rather than one focused on a particular, perhaps overly narrow range of emissions.
There is no question that we are re-examining the nature of the SETI search as we grapple with such issues. In radio frequencies, we are most likely to be able to receive a directed signal, which means that here — or in the optical range as well — our best bet is to find extraterrestrials who already have an interest in communicating with us. Again, we have no reason to assume that alien cultures will feel such a need. Extending SETI into the realm of deep-sky observation (optical SETI is already doing this), using parameters that are both carefully selected yet open to anomalous result, seems a natural and logical development.
LOFAR and the Quest for Synergy
Which brings us to LOFAR, the Low Frequency Array that is now planning to link radio detectors across Britain, France, Holland, Sweden and Germany. LOFAR studies a wide range of frequencies between 20 MHz and 80 MHz, and again between 120 MHz and 240 MHz. Its primary function is scientific, notes Robert Nichol of Portsmouth University in The Guardian:
“We will be looking for all sorts of different things with Lofar,” added Nichol. “We will make surveys of the skies to look for unexpected events; for things that go bump in the night, as it were. We will also be able to study the universe’s childhood years. We know a lot about the Big Bang, when the universe was created 13 billion years ago, and a lot about it now. But its early childhood years, around 500 million years after the Big Bang, remain a mystery.”
But Nichol adds that extraterrestrial broadcasts could potentially be found by LOFAR’s detectors. LOFAR, in other words, is a project dedicated to basic research that could have SETI ramifications on the periphery, and I think that’s about the right mix. Those of us who doubt SETI will produce a confirmed extraterrestrial civilization any time soon would still like to see synergy between ongoing science and the attempt to make such discoveries. And we’d like to be proven wrong in our SETI pessimism. Whichever wavelengths we’re studying, whatever objects in the heavens, let’s keep our minds open and hope to be surprised.
jim,everyone,yes this is a great thread of conversation! and i sure do believe that we should colonize space much more than “just” huddle around a dyson sphere! naturally the oort cloud is a place to have a look at too.also,when we start thinking about subjects like the multiverse…then,we REALLY see how big space actually is!! and,alot of fine minds do believe in such today!let me repeat something i just said to another friend who does not post here.we should all read dr michio kakus latest book physics of the impossible! perfect for us! and lol no as i usually point out when i reccommend a book – no i do not get a commission. paul, i know you are way ahead of me on this but given the thread of this conversation i just couldn’t help but mention that book to everyone! all the best everyone! your friend george
I don’t see why interstellar travel would be an alternative to a dyson sphere. Though I doubt any civilization would bother with dyson spheres in any event. A dyson swarm combined with interstellar colonization seems to me the best method of ensuring survival.
A sphere located 1au from the sun would have a surface area of 2.83E17 sq kilometers. If you were to build a space habitat, capable of replicating itself, that had 1 sq kilometer of solar collectors then it would need to replicate 59 times to cover the entire surface of that sphere in solar collectors. If each replication took 100 years it would take 5900 years to create such a swarm.
After the swarm was built they could easily spare a few billion that could be sent to other solar system. 1 per star. Such a civilization would be able to use all the energy within matter so getting those colonies up to 1 per cent light speed should be doable. 10 million years and every star in the galaxy would have at least 1 element of a dyson swarm. 6000 years after that every star in the galaxy would have a dyson swarm.
Building such swarms would not exclude them from also utilizing oort/kuiper belt objects.
The material for building the swarm elements would come from mining the star itself, assuming you even wanted a star and didn’t just dismantle the whole thing and use its mass as a fuel source.
Unless there is a way to create pocket universes, or unless there is an infinite number of universes with methods of getting to them, we will have to learn how to live within our means at some time.
Hi George and all other Folks;
Great discussion!
Regarding colonizing other star systems, I am going to be really thrilled when the first modules of the planned permanently manned lunar outpost are installed on the Moon. Once this outpost is up and running, I think more such outposts will be established and soon we will have a full scale lumar civilization. Mars will be next for colonization and then it will be outward from there. Funny thing is, when these outpost and colonies are up and running, in a sense, these extraterrestrial settlers will be ETs relative to us back here on Earth. As the human race expands out into the Milky Way Galaxy and then to galaxies beyond, I am sure evolutionary processes will effect our desendants in terms of their body shape type, physiological, psychological, emotional, and intellectual evolution.
Thanks;
Your Friend Jim
In reply to Ronald’s comments about the practicality of colonizing the Ort cloud, I would point out that it is a lot easier than interstellar colonization. Ort cloud bodies are separated by an average distance of 1 au. Trip distances for colonization purposes would be in the order of 10 to 100 au, which could be accomplished by ships with a high specific impulse drive that would have power level in the order of 100 megawatt/100 ton. The colonization would be gradual spreading through the cloud over hundreds of years.
As you’ve seen from the discussions, the power requirements for interstellar travel are in the order of 1000 Terawatts. This is over one hundred times our total power consumption at the moment. If you look at the requirements for a nuclear powered Mars vessel, something possible with a major effort we are looking at the 20-100 Megawatt range. Interstellar travel will require a million times that. Assuming the same level of effort, a 1000 TW vessel should be buildable by a society with about a million times our current power consumption level, 10^18 watt, two orders of magnitude over a Type I civilization level, or about 700 years into our future at a 2% power consumption growth rate.
The entire amount of energy falling on Earth is 10^16 watt so unless we can radically reduce the energy needed for interstellar travel, interstellar travel will only be accomplished by a civilization whose vast preponderance is off Earth. (Any attempt to have a 10^18 watt civilization on Earth would rapidly reduce the planet to molten slag with its waste heat.)
I would assume that the Ort cloud would not be colonized by flesh and blood human, but by some sort of artificial descendent.
I also assume that when interstellar colonization is attempted, it will be done by the cheapest method, which would be to send some sort of Von Neuman machine to the destination that would build a receiver station and that the contents of the intelligence’s mind would be beamed to its destination.
Dave.
Hi David
That’s pretty much what we’d expect, though history has taught us to expect the unexpected. For example, what if humans can’t be beamed as information from place to place? There’s a lot of unknowns at present in this whole discussion.
@Dave:
1000 TW is about 60-70 times our present energy consumtion level (of about 15 TW).
Why would a society need to have ‘a million times our current power consumption level’, in order to achieve this?
Besides, how do you get to this high power requirement?. I have read considerably more modest estimates over time, based on a 1000 tonne space craft at 0.1 c, driven by laser sail (on the order of tens to a few hundred TWY total energy requirement, at 50% efficiency of energy generation/conversion).
Elaborating a bit further:
even assuming Dave’s (high) power requirements, economic fact is that as a society develops greater prosperity, it is able and willing to spend relatively more on ‘luxury items’, that is anything beyond what is strictly needed for its survival. Already a great percentage of our present-day energy consumption is spent on luxury things and this is just increasing.
Even if we assume that future global society would be willing and able to spend ‘only’ 1% of its total energy expenditure on interstellar travel, it would require a total global energy generating capacity of 100.000 TW or about 6000 times present level. At 2.5% growth this level will be reached within 360 years.
If made a global priority and a dedicated project, permitted to consume say 10% of global energy, it would require a total global energy generating capacity of ‘only’ 10.000 TW or about 600 times present level. At 2.5% growth this level will be reached within 265 years.
Again, this assumes the high energy requirements for such an undertaking, as quoted by Dave (1000 TW), and ‘only’ 2.5% annual energy consumption growth. If and when (advanced forms of) fusion are mastered, much greater growth and ultimately higher levels are entirely feasible, without Dyson spheres (though swarms/fleets of solar panels might still be a good idea anyway).
(darn, this is my 3rd in a row, I promise it will be my last on this topic)
I am strongly convinced that future interstellar exploration (initially mini-robotic, later settlement) mainly hinges on two fundamental preconditions:
1) the discovery and detailed telescopic study of earthlike planets near solar type stars, be it inhabited, biocompatible (water, right temp, etc.) or at least reasonably terraformable, which will tantalize humankind and open the political and financial floodgates for Manhattan Project or Apollo Project equivalent initiatives. Gradual Oort belt settlement, no matter how more realistic and doable, would most probably never achieve the same level of collective fascination and sense of purpose.
2) the mastering of nuclear fusion, preferably advanced D-He3 type, which will enable and justify such energy expenditure (see previous posting). Realize that intercontinental air travel for a few hundred dollars (or euros), or any space flight, would have seemed unthinkable, not just technically but also economically, a few centuries ago.
Other requirements, such as technological development, economic prosperity and political stability, are secondary and will probably also ensue from the above two.
As stated above in this discussion, the energy requirement, though fundamental, may at a certain level simply not be a limiting factor anymore. Sense of purpose and destiny will always be.
Hi Ron
The 100 trillion for the last MS stars was correct – while pristine gas in the ISM will decline, higher mass stars blow off most of their mass and so the ISM will have a supply of gas until stars are too low mass to resupply it. According to Fred Adams and Greg Laughlin’s “Five Ages of the Universe” that’s between 10-100 trillion years from now, also roughly when those low mass stars start evolving off the MS and into helium-dwarf obscurity.
One effect of increasing metallicity in the ISM will be changed evolution of low mass stars – the minimum stellar mass will drop slowly to ~ 0.04 solar masses. Enhanced opacity in collapsing molecular clouds also means the initial mass function becomes increasingly biased towards lower masses. Also enhanced metallicity shortens MS lifespan and increases opacity, so low mass stars might form red giants more easily and at lower masses than the current ~ 0.25 solar masses. Overall the effect will be to enhance recycling of the unused gases in stars, eventually using it up at very high efficiency.
I also expect helium stars to form directly from the ISM eventually, but they will be very short-lived compared to similarly massed hydrogen/helium stars. Helium burns hotter and faster and produces somewhat less energy as it turns into carbon. Carbon stars could form via collisions between degenerate dwarfs and they will be incredibly bright and short-lived in that far distant age dominated by red dwarfs and barely glowing ultra-low mass stars. Supernovae will still occasionally erupt as white dwarfs collide and surpass their Chandrasekhar limit.
So expect a lively Galaxy even as it approaches ~ 400,000 Galactic years of age. But eventually it will go dark.
jim,yes branches of our own species may incredibly be “aliens”,at least to us someday! good sf story in there someplace! also saw above that colonization of the oort cloud would be easier than interstellar! absolutely correct.that is a good idea on the face of it i am sure. thanks eveybody. your friend george
(I apologize for not keeping my promise to shut up here, but darn, this is all so interesting)
@Adam: will the shorter lifespan of stars induced by high metallicity not be countered by the average lower mass, i.e. eventually a galaxy consisting of mainly and increasingly red dwarfs?
I read an intersting article recently (I think in Astronomy, not sure) that in about 100 billion years the Big Bang will hardly be detectable, since the universe is expanding at the level beyond the super cluster, resulting in that 1) all galaxies within our supercluster will have merged into one super galaxy and 2) because of cosmic inflation other superclusters will have disappeared beyond the horizon of our visble universe (comoving frontier?).
So our visible universe will be one supergalaxy dominated by red dwarfs. Still very long lived though, in view of Adam’s comments above.
One afterburner with regard to Dave’s postings, I couldn’t help it and did some quick calculations:
Using Dave’s own data: 100 billion comets would require 10^20 W = 100 million TW.
Let’s say that 1/thousandth of that, i.e. 100 million comets, would give us the equivalent of one earth surface or at least the land area of it. That would still require 100 thousand TW. A hundred times as much (!) as it takes to get us to the stars, again according to Dave’s own data of 1000 TW. For about one earth living area equivalent.
Of course the (only?) advantages would be that they are closer and it can be done incrementally over time, comet by comet, risk-spreading and learning as we proceed. But then what would we get: comets, platforms in the ocean in the dark cold outer regions of our solar system, and very lonely, still about 1 AU apart. And what is there to get? Will such small colonies ever be self-sustaining?
Apart from the tremendous inherent risk of small islands in relation to stochastic extinction events (i.e. shit happens, same reason why we don’t find viable populations of larger animals on small islands).
I do not believe that anything human will ever want to live there, maybe work for a limited time, but not live.
It would be much (MUCH) more feasible to settle Mars, the Jovian and Saturnian moons and the asteroids.
Humans, or anything like it, will want to settle planets, like living, making love and procreating.
That’s why I believe that our future is in settling (and terraforming) other planetary systems, planet by planet, system by system.
That’s also why I strongly hope that near-future research will reveal earthlike or at least biocompatible/terraformable planets near Alpha Centauri A and B. They are by far our best bet within a dozen light years at least.
Forget about the comets, and go for the real prize, the stars and their planets.
Some comments on Ronald’s last post.
First off, I took the 1000 TW figure from earlier posts on this subjects, but I suspect as time human ingenuity will find way to lower the energy cost of going to the stars in the future. However, I would like to point out that 15 TW society has trouble mustering the will to produce a hundred megawatt spaceship to go to Mars. That’s expending 1 part in 10^5 of our total energy expenditure. What makes you think in the future we will do significantly better?
As for the desirability of comets as a home, while they may not be particularly appealing to humans, if you are an AI with a superconducting brain bathed in liquid hydrogen, they look just cozy.
Incidentally, your comments on the desirability of commentary habitation, could be equally applied to the planets you mentioned. (Except for a few hardy individuals, Humanity doesn’t like dwelling in even the more inclement places on Earth. What makes you think anybody will want to settle on a radiation soaked ice-ball around Jupiter?)
Your points about the dispersal of comets are well taken. Such a society would perhaps resemble Pacific Island society with small dispersed populations separated by both long communication and travel times. Not all the bodies will be small though. I was reading recently that astronomers examining the out reaches of our solar system expect eventually to find Mars and even Earth sized bodies out there.
Dave.
Hi Ron & Dave
Some theories of formation of the Ice Giants imply tens of Mars to Earth scale bodies out in the Oort, scattered by Uranus and Neptune during their formation.
A swarm of a billion habitats each holding a thousand people would intercept a tiny amount of the star’s light Admittedly this would not represent a true Dyson swarm, but the amount of material available for construction (without assuming transmutation) is surely limited.
Such a limited swarm would resemble a (strangely regular?) debris disk around a distant star; we might have seen some already. I doubt that swarms that cover the star completely would be built very often, if at all. A swarm with a trillion inhabitants would be a remarkable thing- and a fraction of the energy of such a swarm could send innumerable interstellar missions to do the same thing to other stars.
I think limited swarms are quite likely to occur in our own future- and that suggests that the alien equivalent might be out here waiting to be detected.
Hi Folks;
Thinking of the long term survival of our species and infrastructure, it occurred to me to look back to the socalled first Planck Time interval where temporal resolution at a finer level is considered undefinable.
Now, what if by chance, during this first Planck time interval, a whole history played out, perhaps even an infinite casually, weakly casually, and/or indetermanently linked sequence of events, even an infinite number of such sequences occuring in parallel with causal coupling occuring between these sequences at various points in the sequences.
One of our current contributers, Forrest, has developed a brilliantly creative explanation of the origin and evolution of our universe in which time is simply defined by change. Well, perhaps an infinite amount of time went by during the socalled Planck Era of our universe as defined by an infinite series of franetic particle interactions for which change would be defined. If such is the case, there may have occurred multiple phase changes, perhaps an infinite series of such phase changes such as that which gave rose to inflation and the symmetry breaking events that lead to the gradual sequential seperation of the four known fundamental forces.
Perhaps the evolution of the Big Bang from the Planck Era onward occured as is suggested by the current Big Bang models even though any such sub-Planck scale behavior may have occured. The occurance of any such sub Planck scale events might have been completely erased as to any information we would be able to acquire in an analogous manner that hidden quantum variables might actually exist but in such a way that we would not have access to them and in such a way that the thermodynamic information of any hidden quantum variables remains perhaps safely locked from our access forever.
Even if our universe did experience any such sub-Planck scale behavior, I do not see why the existence of an ensemble, and perhaps even an infinite number of casually decoupled seperate universes might exist.
Thanks;
Jim
jim thank you fantastic concept,lol, as usual ! there is always just sooooooo much that we do not know!research indeedWILL BE never ending! thank you george
Hi George;
Thanks for the enthusiatic endorsement.
It occured to me that the formation of such universes with sub-Planck interval histories might be occuring ubiquitously within physical eternity. I use the word physical eternity because time relative to each universe outside of each universe would have no meaning. Presumably for non-casually connected or ontologically and existentially decoupled universes, time within each such universe would have no meaning outside of each such universe with respect to the temporal interior of each such universe.
Just what would this realm of physical eternity be? Might there be an infinite number, an undefinable cardinality of such physical eternities wherein each such eternity is casually, eternally, existentially, and ontologically decoupled from all of the other such eternities. Perhaps there is an over-arching ontological principle which underwrites ontologically and existentially the meaning, truth, and integrety of such a cardinality of infinity of eternities which might labeled hyper-eternity, trans-eternity, super-eternity or what have you. Perhaps each such over-arching ontological principles, Or-1, are part of a family of a given cardinality of such principles Sigma Or-1. Perhaps each family Sigma Or-1 is a member of yet another higher level family Or-2 which is just one member of the set Sigma Or-2, and so on through Sigma Or – (Aleph 0) and beyond and onward forever.
I bring up these far out concepts as just an example of taking the concept of the multiverse to an extreme, but in the minds of any existent directing higher power, just one stepping stone in eternity.
Thanks;
Your Friend Jim
If there is one galaxy we know of that has any possibility of
being sculpted by advanced ETI with a cosmic sense of
aesthetics, it would be this one:
http://www.universetoday.com/2008/04/21/ngc-3718-dietmar-hagar/
The ghost of a dwarf galaxy: fossils of the hierarchical formation of the nearby spiral galaxy NGC 5907
Authors: David Martinez-Delgado (IAC, MPIA), Jorge Penarrubia (Univ. Victoria), R. Jay Gabany (Black Bird Observ.), Ignacio Trujillo (IAC), Steven R. Majewski (Univ. Virginia), Michael Pohlen (Cardiff Univ.)
(Submitted on 8 May 2008)
Abstract: We present with exquisite detail an extragalactic perspective of an extended stellar tidal stream wrapping around the edge-on, spiral galaxy NGC 5907. Our deep images reveal for the first time a large scale complex of arcing loops that is an excellent example of how a low-mass satellite accretion can produce an interweaved, rosette-like structure of debris dispersed in the halo of its host galaxy.
The existence of this structure, which has probably formed and survived for several Gigayears, confirms that halos of spiral galaxies in the Local Universe may still contain a significant number of galactic fossils from their hierarchical formation.
To examine the validity of the external accretion scenario, we present N-body simulations of the tidal disruption of a dwarf galaxy-like system in a disk galaxy plus dark halo potential that demonstrate that most of the observed tidal features observed in NGC 5907 can be explained by a single accretion event.
Unfortunately, with no kinematic data and only the projected geometry of the stream as constraint, the parameters of our model are considerably degenerate and, for now, must be considered illustrative only.
Interestingly, NGC 5907 has long been considered a prototypical example of a warped spiral in relative isolation. The presence of an extended tidal stream challenges this picture and suggests that the gravitational perturbations induced by the stream progenitor may be the cause for the warp.
The detection of an old, complex tidal stream in a nearby galaxy with rather modest instrumentation points to the viability of surveys to find extragalactic tidal substructures around spiral galaxies in the Local Volume (< 15 Mpc) — with the prospect of obtaining a census with enough statistical significance to be compared with cosmological simulations.
Comments: Submitted to The Astrophysical Journal. High resolution version of the paper, full colour version of the NGC 5907 tidal stream image, movie of the N-body model and IAC press release can be found at: this http URL
Subjects: Astrophysics (astro-ph)
Cite as: arXiv:0805.1137v1 [astro-ph]
Submission history
From: David Martinez-Delgado [view email]
[v1] Thu, 8 May 2008 11:22:26 GMT (739kb)
http://arxiv.org/abs/0805.1137
Hi Folks;
It really just occurred to me for the first time or it reoccurred to me the concept of light sails or beam ships on steroids that could be powered by stellar energy collected by Dyson Spheres.
One can imagine a Dyson Sphere built to enclose the Sun wherein 4 x 10 EXP 26 Joules would be collected per second within some enclosing energy absorbing medium whereupon the energy would be converted back into fusion fuel, antimatter fuel, or even electrical energy stored within future super high energy density storage capacitors. The energy thus collected over about one year would be the equivalent of about 100 trillion tons of mass converted into energy. The collected energy might be used to some how accelerate a 1,000 metric ton beam ship to a gamma factor of 10 EXP 5.5 or 300,000 assuming that the overall efficiency of converting the (10 EXP 17)(10 EXP 17) Joules of beam energy into the kinetic energy of the 1,000 metric ton space craft is roughly equal to [(10 EXP 14)/(10 EXP 3)] EXP 1/2 due to beam relativistic Doppler red shift based losses. Using similar simplified rough order of magnitude estimates, a 10 trillion metric ton ship could be accelerated to roughly a gamma factor of 10 EXP (1/2) or of about 3. Note that these calculational rough estimates are greatly simplified and that in order to get precise results integration is required.
Around other stars, Dyson Spheres could be constructed for the same purpose, however, the beamed energy originating from these extra solar Dyson Spheres could be directed onto an incoming ship at a precisely pre-arranged time onto a negative index refraction energy collector such that the space craft would, in theory, be accelerated or pulled forward by the incident extra solar beam(s) whereupon the greater the incoming velocity of the craft, the greater the force of pull. As you can imagine, tremendous gamma factors could be achieved as a result.
Perhaps some way to decelerate the space craft could be devised wherein electrodynamic ambient interstellar space energy or incident beam energy could be absorbed and converted back into mass on the space craft. Another option for craft deceleration is to simply shine the extra solar beams on a reflective surface installed aboard the space craft. Additionally, the beam from the Sun based Dyson Sphere could be used to power a reverse thrust mechanism aboard the space craft.
Thanks;
Jim
What Happens When a Galaxy Eats Its Neighbor?
New images show that two rivers of stars—and possibly dark matter—are all that remain of one dwarf galaxy.
by Tyghe Trimble
published online September 14, 2008
Image Credit & Copyright: R Jay Gabany
The last remnants of a dwarf galaxy circle the spiral galaxy that tore it apart. Two rivers of stars—and possibly dark matter—are all that remain of the low-mass dwarf after it was unraveled by the gravity of the much larger spiral, NGC 5907.
Astronomers have noted that such streams of stars are relatively common in the outer regions of spiral galaxies, a phenomenon that has been observed on the outskirts of the Milky Way as well as around the nearby Andromeda galaxy.
This image, taken by accomplished astrophotographer R. Jay Gabany in collaboration with David Martinez-Delgado from the Instituto de Astrofísica de Canarias (IAC) and his international team, shows for the first time in intricate detail the aftermath of a large galaxy destroying and consuming its dwarf neighbor.
http://discovermagazine.com/2008/oct/14-what-happens-when-a-galaxy-eats-its-neighbor
A very interesting and very scary thought:
http://eg.orionsarm.com/xcms.php?r=oaeg-view-article&egart_uid=48fe49fe47202
Another explanation of the Fermi Paradox? Is this how Kardashev
Type II and III civilizations might get rid of the competition without
ever leaving their homes?
IRAS-based whole-sky upper limit on Dyson Spheres
Authors: Richard A. Carrigan Jr
(Submitted on 14 Nov 2008)
Abstract: A Dyson Sphere is a hypothetical construct of a star purposely cloaked by a thick swarm of broken-up planetary material to better utilize all of the stellar energy. A clean Dyson Sphere identification would give a significant signature for intelligence at work.
A search for Dyson Spheres has been carried out using the 250,000 source database of the IRAS infrared satellite which covered 96% of the sky. The search has used the Calgary data collection of the IRAS Low Resolution Spectrometer (LRS) to look for fits to blackbody spectra.
Searches have been conducted for both pure (fully cloaked) and partial Dyson Spheres in the blackbody temperature region 100 < T < 600 deg K. Other stellar signatures that resemble a Dyson Sphere are reviewed. When these signatures are used to eliminate sources that mimic Dyson Spheres very few candidates remain and even these are ambiguous.
Upper limits are presented for both pure and partial Dyson Spheres. The sensitivity of the LRS was enough to find solar-sized Dyson Spheres out to 300 pc, a reach that encompasses a million solar- type stars.
Comments: 32 pages, 8 figures
Subjects: Astrophysics (astro-ph)
Report number: Fermilab Pub-08-352
Cite as: arXiv:0811.2376v1 [astro-ph]
Submission history
From: Richard Carrigan Jr [view email]
[v1] Fri, 14 Nov 2008 16:36:53 GMT (517kb)
http://arxiv.org/abs/0811.2376
Hi all,
As some other posters noted before I think we must seriously consider scenarios of the energy needs of post Singularity civilizations!
What amounts of energy will it (they?) need? Calculations based on current growth of population and it’s energy needs are in my humble opinion irrelevant!
We have to imagine the possible form of this civilization (computronium, nanotechnology, holograms etc) and for every possible scenario figure out if a Dyson sphere (and even interstellar traveling) is required.
Regards,
kLee
http://arxiv.org/abs/astro-ph/0001154
The Stellar Content of NGC 5907’s Dark Matter Halo
Michael Liu, Francine Marleau, James Graham, Stephane Charlot, Penny Sackett, Steve Zepf
Comments include:
“What they did not see – lots of stars – has led them to conclude that the halo is composed of a weird population of stars, mostly dim dwarfs too faint to see from Earth. Most galaxies contain a mix of bright giant stars and dim dwarf stars, with about half of the light coming from each group. If the halo of NGC 5907 contained a mix similar to that in our own galaxy, the team would have seen hundreds of bright giants in the field of view. Instead they saw only a handful of bright stars.
The best explanation of the team’s observations is that at least 20 times more light comes from dwarfs than giants in the halo of NGC 5907.
“Our results force us to turn to more esoteric descriptions of the stellar content of NGC 5907’s halo,” said Michael Liu, a graduate student at UC Berkeley and lead author.
“In particular, our data combined with the measured colors of the halo suggest a very metal-poor stellar population with an enormous excess of faint dwarfs.”
http://www.universetoday.com/93746/galactic-archaeology-ngc-5907-the-dragon-clash/
Galactic Archaeology: NGC 5907 – The Dragon Clash
by Tammy Plotner on February 23, 2012
The sprawling northern constellation of Draco is home to a monumental galactic merger which left a singular spectacle – NGC 5907. Surrounded by an ethereal garment of wispy star trails and currents of stellar material, this spiral galaxy is the survivor of a “clash of the dragons” which may have occurred some 8 to 9 billion years ago. Recent theory suggests galaxies of this type may be the product of a larger galaxy encountering a smaller satellite – but this might not be the case. Not only is NGC 5907 a bit different in some respects, it’s a lot different in others… and peculiar motion is just the beginning.
“If the disc of many spirals is indeed rebuilt after a major merger, it is expected that tidal tails can be a fossil record and that there should be many loops and streams in their halos. Recently Martínez-Delgado et al. (2010) have conducted a pilot survey of isolated spiral galaxies in the Local Volume up to a low surface brightness sensitivity of ~28.5 mag/arcsec2 in V band. They find that many of these galaxies have loops or streams of various shapes and interpret these structures as evidence of minor merger or satellite infall.” says J. Wang of the Chinese Academy of Sciences. “However, if these loops are caused by minor mergers, the residual of the satellite core should be detected according to numerical simulations. Why is it hardly ever detected?”
The “why” is indeed the reason NGC 5907 is being intensively studied by a team of six scientists of the Observatoire de Paris, CNRS, Chinese Academy of Sciences, National Astronomical Observatories of China NAOC and Marseille Observatory. Even though NGC 5907 is a member of a galactic group, there are no galaxies near enough to it to be causing an interaction which could account for its streamers of stars. It is truly a warped galaxy with gaseous and stellar disks which extend beyond the nominal cut-off radius. But that’s not all… It also has a peculiar halo which includes a significant fraction of metal enriched stars. NGC 5907 just doesn’t fit the patterns.
“For some of our models, we assume a star formation history with a varying global efficiency in transforming gas to stars, in order to preserve enough gas from being consumed before fusion.” explains the research team. “Although this fine-tuned star formation history may have some physical motivations, its main role is also to ensure the formation of stars after the emergence of the gaseous disc just after fusion.”
The Secret History of the Splinter Galaxy
By Phil Plait
Posted Tuesday, April 9, 2013, at 8:00 AM
Spiral galaxies have an interesting property: They’re flat. When you see them face-on, you can take in their full spirally goodness. But if they happen to be oriented edge-on to us, they can look nearly as thin as a knife’s edge.
NGC 5907 is a great example of that. Located roughly 40 million light years away—fairly close by as galaxies go—it is very nearly sideways with respect to us, and so thin it was given the nickname “The Splinter Galaxy”.
Full article and astrophotos here:
http://www.slate.com/blogs/bad_astronomy/2013/04/09/spiral_galaxy_photo_ngc_5907_ate_another_galaxy.html