Exobiology / Science -> Homeclick!

Cette page en françaisCliquez!

Science about ET in the galaxy:

Physicist Freeman Dyson suggested in the early 1960s that an advanced civilization would build a vast shell around its star. Such a shell, now called a "Dyson sphere," would absorb the star's energy for the civilization's use. Stars showing such characteristics have been detected.

Sphère de Dyson

Dyson spheres:

Nikolai Kardashev and the classification of ET civilizations:

In the last decades, several scientists have wondered what source of energy might be used in the far future, or what source of huge quantities of energy might be used by a very advanced extra-terrestrial civilization.

In 1964, the prominent Soviet astronomer Nikolai Kardashev was a member of the group of Russian scientists searching the heavens for traces of extraterrestrial life. He speculated about the kinds of advanced alien society that might exist elsewhere, and had the idea that the most useful method of classification would be to divide such theoretical societies according to their energy consumption:

Our own earth is on its way of becoming a Phase I civilization, but it still has a long way to go.

Freeman Dyson and the Dysonspheres:

Freeman Dyson is an English born, American physicist who has become a kind of guru for science fiction fans, because of the amazingly wide ranging nature of his mathematically based speculations of the nature of our universe and that life may exist in it. Also, Dyson has been prepared to publish his conjectures in sober scientific journals, where they have reached an audience which might have dismissed then out of hand if they had appeared in, say, a science fiction magazine in the first instance.

In 1959, in a short paper published in Science entitled "Search for Artificial Stellar Sources of Infra-Red Radiation", Dyson revolutionized science-fiction thinking overnight with this new speculative idea: if there are technological societies on other planetary systems, then they would use more energy every year as their society evolves, just as we do. Even a modest growth rate of 1% annually in the consumption of energy, much lower than our own doubling of energy consumption every decade, would lead to an increase of 1012 (1000 billion) in only 3000 years.

Dyson had this idea before Kardashev established his terminology, but he was clearly talking about the transition from a Phase I civilization to a Phase II. Earth could not support a growth even a tiny fraction as large as this. The only way this growth could be sustained would be to use all the energy of the Sun, and the only way, said Dyson, to trap all the Sun’s radiation would be to build a sphere around it.

An idea originating from early speculative science fiction:

The notion of such a giant sphere was actually originally proposed in 1937 in the science fiction novel "Star Maker" by Olaf Stapelton:

"Every solar system [was] surrounded by a gauze of light traps, which focused the escaping solar energy for intelligent use."

However such light traps are are now refered as "Dyson Spheres" by all science fiction readers. If such a sphere were built in our own solar system, it would probably be built so that its radius would be the same as the present distance of the Earth from the Sun. We would live on the inside surface of the sphere, facing the Sun. It would always be noon. There would be drawbacks. There would be no gravity to start with unless we generated it artificially by spinning the sphere, but then would restrict the comfortably habitable zone to a belt round the sphere’s equator. Or perhaps, by then, we shall know how to generate gravity directly. There would be plenty of room. The surface area of the inside of the sphere, would be approximately 1 billion times that of Earth.

Speculators have said that raw materials are at hand: we might start by using the asteroids, and later on use Mars and then Jupiter. Jupiter alone would give us enough mass to make the sphere at least 3 meters thick. We can hardly conceive of such a plan in terms of our present day technology, but this is different in a high-energy far future, with around 1000 billion times as much energy to use we have now.

In practice the idea of an unbroken sphere would probably not work. Its very rigidity would subject it to tremendous amounts of stresses that would probably tear it apart. But we need not go all the way. A useful compromise might be to build a spherical shell of individual worldlets perhaps a million of them each one orbiting independently. A lot of sunlight would leak to the gaps, but we would retain a great deal. Waste heat, which as on Earth would largely take the form of infrared radiation, would be pumped out through the shell away from the Sun. It follows and this was Dyson’s point that, if we are seeking intelligent life elsewhere in the galaxy, we should keep an eye out for objects radiating in the infra-red. Perhaps some might be Dysonspheres. From a visual sight from the outside a Dysonsphere would look like a dully luminous, giant red star. And it would emit unusual amounts of infrared waves.

Stars with excess infrared emission:

So, did we detect any star which would emit excesses of infrared, and might - repeat, might - have something to do with Dyson's idea?

Here is an American Astronomical Society publication:

Session 47 - Circumstellar Disks & Shells.

Display session, Thursday, January 08
Exhibit Hall,

[47.07] New Emission-Line Stars with Infrared Excesses

C. L. Mulliss, A. S. Miroshnichenko, K. S. Bjorkman, N. D. Morrison (U.Toledo)

We present the results of high-resolution spectroscopic observations of four late B-type stars with strong far-IR excesses (HD 4881, HD 5839, HD 224648, and HD 179218) obtained with the 1-meter telescope of the Ritter Observatory in a spectral range of 5300 - 6700 ÅDouble-peaked H\alpha\ emission line profiles are detected in HD 4881 and HD 5839, while HD 224648 displays no emission in H\alpha. The remarkable variations of the H\alpha\ line profile we found in HD 179218 are also observed in some classical Be and Herbig Ae/Be stars. Parallaxes measured by the HIPPARCOS satellite were used to determine positions of the stars in the HR diagram. The former two stars are located nearly 1^m above main sequence and are most likely newly discovered classical Be stars. HD 224648, having very small near-IR excess, is probably a young main sequence star. HD 179218, which exhibits the largest near- and far-IR excess in the sample, is probably a pre-main-sequence Herbig Be star. This star does not belong to any known star formation region, but it shows a compact nebula which is similar to those of isolated young intermediate-mass stars.

So HB179218 has the largest near and far infrared excess. It shows a "compact nebula" around it. We are left with the question of the artificial or natural nature of this nebula. If natural, it can explain the excess infrared, being heated the star.

But if someone would issue a statement such as "no Dyson sphere has ever been detected", we must answer: "is this so certain?"

Further discussion:

Here are three searches for Dyson spheres at http://www.seti-inst.edu/searches/searches-list.html:

SEARCH FREQ.(MHz):8.5 microns - 13.5 microns
COMMENTS:Search for IR excess due to Dyson spheres around solar type stars. Target stars were chosen because too faint for spectral type.

SEARCH FREQ.(MHz):37x10**3
FLUX LIMITS (W/m**2):T/T =< .01
COMMENTS:Lack of fluctuations in 3K background radiation on angular scales of 10**-2 Strd. rules out optically thick Dyson spheres radiating more than 1 solar luminosity within 100 pc.

SEARCH FREQ.(MHz):1612.231
COMMENTS:Remote observation (by VLA staff) of IRAS source near galactic center to determine if source could be nearby Dyson sphere. Source confirmed as OH/IR star.

In short, SETI seems to have searched for Dyson spheres and did not find fitting to their criteria any as it seems. But there has not been any very thorough search for them either.

However, there has been news items such as this one, extremely puzzling, but it seems that the very idea of the Dysonsphere has been forgotten...

Unfortunately, astronomers and SETI researchers continue to look for signs of life assuming human perspectives, that is, visible stars, radio wave base communication directed towards us, rather than perspectives dictated by the limits of the laws of physics. Only whole sky surveys, with long exposure times in the mid-far IR ranges are likely to detect low temperature Dyson shells. Remember that the more advanced type II civilization would have less losses of energy, thus low temperature Dyson shells. Unfortunately, even expensive telescopes, like SIRTF, that will not be available until 2002, the detectors for these wavelengths, typically, Si:As, Ge:Ga and stressed Ge:Ga are still very primitive. It is doubtful that even very advanced telescopes, still in the planning stages, would have the capabilities required to provide definitive evidence for or against these objects.

Discoveries in March 2006

In March, 2006, several scientific teams looking at Celpheid stars, outside our own galaxy, giant stars that pulsate every few days, have found three of them to be surrounded by a fairly bright layer of matter, a "cocoon". One team led by Antoine Mérand of the Observatoire de Paris and CHARA Array at Mt. Wilson Observatory in California has found similar cocoons around the Northern Star and Delta Cephei. Pierre Kervella of the Observatoire de Paris, who is the main author of the report of the discoveries in the Journal of Astronomy and Astrophysics, found such an envelope around L Carinae, the brightest of Cepheid in the sky, 180 times larger than the Sun, while one of these enveloped stars is 400 times brighter than the Sun.

These cocoons are about two to three times larger than the stars and about 4 percent as bright, which is very bright considering that these pulsating stars themselves are incredibly radiant.

Previously, astronomers had found hints that some Cepheids had envelopes, including around one called RS Pup. But now, as they looked at more Cepheids, it appears that it is a widespread phenomenon.

The astronomers are quite baffled at the discoveries. They would have expected that these cocoons would burn. Currently, they have no explanation for the phenomenon. None of them seems to have suggested of thought of Dysonspheres, and there is no evidence that these cocoons are Dysonspheres - read this page from the top - however, until some theory can explain the phenomenon, I thought it was worthwhile mentioning this discovery here anyway.

Discovery in 2016

In 2016, things have changed and astronomers do not ridicule too much the possibility that the anomalies of Tabby's star" could be caused by a Dysonsphere. However, by the end of 2017, the orbiting dust cloud hypothesis gained a lot of weights.


No conclusion either positive or negative can be made at for now.


Valid XHTML 1.0 Strict

 Feedback  |  Top  |  Back  |  Forward  |  Map  |  List |  Home
This page was last updated on January 12, 2018.