On the possibility of the Dyson spheres observable beyond the infrared spectrum Osmanov Z. & Berezhiani V. I. School of Physics, Free University of Tbilisi, 0183, Tbilisi, Georgia ABSTRACT In this paper we revisit the Dysonian approach and assume that a superadvanced civilisation is capable of building a cosmic megastructure located closer than the habitable zone (HZ). Then such a Dyson Sphere (DS) might be visible in the optical spectrum. We have shown that for typical high melting point meta material - Graphene, the radius of the DS should be of the order of 1011cm, or even less. It has been estimated that energy required to maintain the cooling system inside the DS is much less than the luminosity of a star. By considering the stability problem, we have found that the radiation pressure might stabilise dynamics of the megastructure and as a result it will oscillate, leading to interesting observational features - anomalous variability. The similar variability will occur by means of the transverse waves propagating along the surface of the cosmic megastructure. In the summary we also discuss the possible generalisation of definition of HZs that might lead to very interesting observational features. Subject headings: Dyson sphere; SETI; Extraterrestrial; life-detection 1. Introduction which are capable of utilising the total energy of their host star (Level-II civilisation in the Kar- A recent revival of interest to the search for ad- dashev scale (Kardashev 1964)), then they could vanced extraterrestrial civilisations has been pro- have built a relatively thin spherical shell (Dyson voked by the discovery of the object KIC8462852 sphere (DS) with radius ∼ 1AU surrounding the observed by the Keppler mission (Boyajian et al. star. The author has shown that on the mentioned 2016). According to the data, the flux coming distance the internal surface of the DS will be in from the mentioned object has been characterised the habitable zone (HZ). Therefore, the tempera- by dips of the order of 20%, which automati- ture of the megastructure will be of the order of cally excludes existence of a planet shading the 300K, which means that it will be visible in the star. It is worth noting that the detected flux infrared spectrum. has an irregular character, which has been anal- For finding the infrared DSs the monitoring ysed in detail and it has been shown that such a of the sky has been performed by several in- arXiv:1804.04157v1 [physics.pop-ph] 11 Apr 2018 behaviour might not be caused by any measure- struments (Jugaku & Nishimura 2002; Slish 1985; ment errors. Such a strange emission pattern of Timofeev et al. 2000) although no real candidate KIC8462852 and some other similar stars has been was found. In the beginning of the last decade analysed in a series of papers in the context of a new series of investigation has been initiated. artificial megastructures possibly constructed by In particular, Carrigan (2009) has examined and a superadvanced civilisation (Wright et al. 2016; analysed the results of IRAS (The Infrared Astro- Schuetz et al. 2016; Harp et al. 2016). nomical Satellite) covering 96% of the sky and 16 The idea of such cosmic mega constructions objects has been identified as potential DSs but it has been considered by Freeman Dyson. In his has been emphasised that the subsequent investi- well known work (Dyson 1960) he has suggested gation is necessary. that if the superadvanced extraterrestrials exist, According to the Kardashev’s classification the 1 Level-III civilisation is the one that is capable of to the star the higher its temperature. Therefore, consuming the whole energy of its host galaxy the observational signature of this DS will be dif- by enveloping each of the star by spheres. This ferent and it might be visible in the optical spec- means that the galaxy will be seen in infrared. The trum, which according to our analysis might ex- search for galaxy spanning civilisations has been hibit anomalous variability. Relatively hotter DSs performed by Griffith et al. (2015) where the au- have been proposed by Sandberg (1999), where the thors analysed the data of the the Wide-field In- author considered the megastructures built for the frared Survey Explorer (WISE) in the high mid reason of supercomputing. 5 infrared spectrum. In total approximately 10 In general, it is worth noting that in the cur- galaxies have been monitored. They have iden- rent paper we consider existence of possibility of tified almost 100 objects which, according to the extraterrestrials with biology similar to ours. But authors, deserve further study. it is clear that this is a very limited approach, the Last two decade researchers actively discuss so-called carbon chauvinism and water chauvinism the reasons of possible failure of conventional ironically coined by Carl Sagan (Sagan 2000). In approach to the Search for Extraterrestrial In- his book he examines the possibility of noncarbon telligence (SETI) (Cirkovic 2008; Bradbury et al. and nonwater-based live that might significantly 2011). Cirkovic & Bradbury (2006) have consid- enrich a methodology of the search for extrater- ered that the so-called Dysonian method to SETI restrials. is not limited by the conventional approach and a The organisation of the paper is the following: wider view to the SETI problems is required. On in Sec. 2 we present major estimates and discuss the other other hand, a good strategy for astron- possible observational patterns of the DSs and in omy is to observe all interesting events in the sky Sec. 3 we summarise our results. in as many channels as possible. Recently a rather different view to the Dysonian approach has been 2. Main consideration published. In particular, in (Osmanov 2016) the idea of freeman Dyson has been extended and the In this section we consider a theoretical model possibility of colonisation of a nearby region of of DSs with reduced radii, estimate corresponding a pulsar by a type-II civilisation was discussed. temperatures and the consequent emission spectra It has been shown that instead of a sphere the and study the stability of the megastructure. extraterrestrials should use a ring-like megacon- Unlike the case examined by Dyson (1960), structions requiring much less material than for where the DSs were located in the star’s HZ in spheres. It has been found that locating in the this section we consider a sphere with higher sur- HZ the rings will be visible in the infrared spec- face temperature, T . This could be quite reason- trum. In the following work (Osmanov 2017) the able, because smaller megastructure requires less possibility of detection of infrared rings by modern material. By assuming the black body radiation facilities has been considered and it was found that one can show that the radius of the DS is given by in the nearby area of the solar system the moni- 1/2 toring of approximately 64 ± 21 pulsars might be L R = ≈ promising. 4πσT 4 In the framework of the paradigm that con- 1 2 2 L / 1000K ventional approaches should be widened, in the ≈ 2.14 × 1012 × × cm, (1) present manuscript we examine an unusual view L⊙ T to the Dysonian SETI. In particular, if a civilisa- where σ ≈ 5.67 × 10−5erg/(cm2K4) is the Stefan- tion has reached the level-II on the Kardashev’s 33 Boltzmann’s constant and L⊙ ≈ 3.83 × 10 ergs scale, then it might have been capable of living in- s−1 is the solar luminosity. As it is clear from side the shell of the DS even if it is not in the HZ of the above estimate the radius is almost one orders the star but closer to it. The smaller the radius of of magnitude less than one astronomical unit, a the DS the less the material it requires. therefore typical size of the DS in the HZ. Here we used it is quite reasonable to search for such megastruc- two assumptions: (I) the surface temperature is tures. On the other hand, the closer the surface less than the melting point of a material the DS is 2 made of and (II) the super civilisation is capable of An important issue we would like to address constructing an efficient cooling system inside the is the stability problem of the DSs. In an ideal shell. Generally speaking, it is clear that a Level- case the star has to be located in the centre of II civilisation might use meta materials with high the sphere, but it is clear that a physical system melting temperatures. In particular, by consider- can remain in the equilibrium state only in the ing graphene it is straightforward to show that to absence of disturbances. In Fig. 1 we schemati- maintain a cold region with a temperature of the cally show the position of the star (point S) and order of 300K the corresponding heat flux power the DS with the centre O. By assuming that the (normalised on the solar luminosity) is given as DS is shifted by x with respect to the equilibrium position we intend to study its dynamics of mo- κS ∆T −6 tion. It is obvious that according to the Gauss’ Pc ≈ ≈ 2.4 × 10 × L⊙ h law the gravitational interaction of the star and the spherical shell is zero. On the other hand, ∆T/h κ S × × × −1 stars emit enormous energy in the form of electro- −1 × 8 ergs s , 70K cm 2.5 10 erg/(cmK) SE magnetic radiation, which will inevitably act on (2) the internal surface of the DS and consequently, where the temperature gradient is calculated for − the part of the surface which is closer to the star ∆T = (1000 300)K = 700K, h = 100cm and will experience higher pressure than the opposite × 8 −1 −1 κ = 2.5 10 ergs cm K is the typical value side of the sphere.