Type III Dyson Sphere of Highly Advanced Civilisations AroundJBIS, a Super Vol. 64,Massive pp.58 B-6262,k 2011 Hole TYPE III DYSON SPHERE OF HIGHLY ADVANCED CIVILISATIONS AROUND A SUPER MASSIVE BLACK HOLE MAKOTO INOUE1 AND HIROMITSU YOKOO2 1. Institute of Astronomy and Astrophysics, Academia Sinica, P.O Box 23-141, Taipei 10617, Taiwan, R.O.C. 2. Chiba University of Commerce, 1-3-1 Konodai, Ichikawa-shi, Chiba, 272-8512, Japan. Email: [email protected] We describe a new system for a society of highly advanced civilizations around a super massive black hole (SMBH), as an advanced Type III “Dyson Sphere,” pointing out an efficient usage of energy for the advanced civilizations. SMBH also works as a sink for waste materials. Here we assume that Type III civilisations of Kardashev classification [1] form a galactic club [2] in a galaxy, and the energy from the SMBH will be delivered to the club members, forming an energy control system similar to power grids in our present society. The energy is probably transmitted by a sharp beam with coherent electro-magnetic waves, which provide a new concept for the search for extraterrestrial intelligence (SETI) via detection of such energy transmission signals. This expands the search window for other intelligences within the Universe. Keywords: Type III Dyson Sphere, Super Massive Black Hole, Energy transmission, Galactic club, SETI 1. INTRODUCTION Through the evolutionary process of the Universe, it is a great However, the energy management was not well discussed. mystery to create life and develop it to highly advanced intelli- gence. Motivated by this mystery, the search for extraterrestrial The purpose of this paper is to study a new system for a intelligence (SETI) has been conducted for a long time, mainly by society of highly advanced intelligences around a super mas- radio signals with negative results so far. Drake recently reviewed sive black hole (SMBH), as an advanced Type III, pointing out this issue [3]. The SETI project has aimed at stars around which an efficient usage of energy for the advanced civilizations. The planets are expected to be a cradle of life for developing intelli- system could provide the intelligences a distinct advantage for gence and advanced technological civilizations. supporting the higher activities in their society and further possible developments. In Section 2, a possible advanced sys- Dyson Sphere is anticipated as a growing stage of advanced tem is described. In Section 3, a new SETI capability inherent civilisations [4]. In this concept, a star is the expected energy to this system is discussed. source to support the activity for a civilisation which has devel- oped around it. Such a system provides a possible means for 2. ADVANCED SYSTEM energy acquisition by a highly civilised intelligence who should require a prodigious amount of energy to develop and maintain the A society of a highly advanced civilization is supposed to civilisation. After using energy, radiation energy from the central require a huge energy to operate the social system. As the star is converted and radiated to lower frequency radiation, e.g., as gravitational energy released by the accretion of matter onto a infrared radiation, from the Dyson Sphere. Jugaku and Nishimura SMBH is huge, a system must be developed to use this energy conducted intensively the searches for Dyson Spheres ([5], refer- in such a society. The condition around a SMBH at the centre of ences therein). Bradbury revisited this concept [6]. galaxy would be more efficient both in extracting energy and exhausting the waste energy for advanced civilizations, than those of a Dyson Sphere [4]. Some active galactic nuclei (AGN) Kardashev mentioned Type III civilizations as the most are extremely luminous, hundreds of times the integrated stellar advanced stage, which controls the energy on a galactic scale luminosity of a whole galaxy. For example, bolometric lumi- [1]. He classified civilizations in three types depending on the nosity of QSOs and Seyfert galaxies is distributed mostly in a technology level with energy consumption which increases range between 1043-1047 erg/s [7]. Mean spectral energy distri- with the development of technology level: butions of QSOs and Blazars are shown in Fig. 3 of Sanders & Type I – technological level close to that of the present Mirabel [8]. The energy is derived from the gravitational en- one, with energy consumption at ~ 4 × 1019 erg/s. ergy of the central SMBH. A huge amount of radiation is generated in a close vicinity of SMBH, where an accretion disk Type II – a civilization capable of harnessing the energy is rotating around SMBH, and the potential energy of the radiated by its own star (i.e., the stage of “Dyson Sphere”), accreting matter is released to form a hot and dense disk. The with energy consumption at ~ 4 1033 erg/s. × size of SMBH is typically measured in units of the Schwarzschild Type III – a civilization in possession of energy on the radius Rs = 2GM/c2, where G and c are the gravitational con- scale of its own galaxy, with energy consumption at stant and the velocity of light, respectively, and M is the mass 44 8 ~ 4 × 10 erg/s. of the SMBH. In a case of M = 10 M~, Rs is only 2 AU 1 Makoto Inoue and Hiromitsu Yokoo (1 AU = 1.50 × 108 km; is the radius of the Earth orbit). The orbiting around the SMBH. They might be scattered from diameter of an accretion disk is likely the size of our solar the original orbit unless they are actively controlled. The system, comparable to Dyson Sphere of stellar scale Type II closest orbit of a star rotating around Sgr A*, the SMBH in civilizations [1], while the energy scale is more than 108 times our Galactic Centre, was at 600 Rs [10]. A possible orbit larger than that, i.e., the integrated stellar energy of the whole would be compromised by the outer extent of the accretion galaxy. disk and innermost orbit of stars. The proper area for the power plants would be around 103-104 Rs, although param- Radiation from the accretion disk will be collected by a eters of the outer edge of accretion disk and innermost mirror system as a Type III “Dyson Sphere.” Waste material stellar orbit are not well understood. and energy could be thrown off toward the central SMBH, and the SMBH would be the final reservoir for all of the waste It is interesting to investigate the energy efficiency at the materials for any civilizations. Thus, the most advanced civili- power plant for further consideration. The dominant energy zations would develop their activities using a SMBH effi- flow is the outgoing radiation from the accretion disk. Some ciently, putting the power plants around the SMBH at the centre fraction of the radiation energy is reflected and focused onto of their home galaxy. We discuss a possible model of such the power plant. The energy efficiency could be a measure for a system, and the possibility to detect indicators of the existence level of civilisation. of the system, or such civilisations. 2.2 Energy Transmission 2.1 Power Plant around SMBH In a galactic club (e.g., [11]), habitants are not necessarily The structures of the power plant basically revolve around the living at the same place as the power plant near the SMBH. The central SMBH in Keplerian motion to form “Dyson Shells.” In power plant could be even remotely controlled from the intelli- an advanced case of Type II, the central star is almost fully gent habitat. In this case, the energy transmission from the covered to form “Dyson Sphere” (see [6]). Here we discuss the power plant to the habitat should be accomplished presumably case of structures partly covered, or the Dyson Shell type, and by electro-magnetic radiation. Selection of the wavelength re- call it a Dyson Sphere. Unlike a stellar environment, or Type II gion is a key in making an efficient energy transmission. The Dyson Sphere, there are complex structures like relativistic photon energy is higher for shorter wavelengths, while absorp- jets, accretion disk and accreting matters, rapidly rotating stars, tion and scattering are stronger at shorter wavelengths. Re- etc., and hence it would be very difficult to construct a fully cently, many gamma-ray sources have been detected in AGNs covered structure, like a system studied by Birch over a large (e.g., [12]). However, as the matter density in the central region gaseous planet (e.g., Jupiter) [9]. However, it is not easy to set of galaxy is higher, absorption and scattering are greater and numbers of power plants with similar distance orbiting around the energy transmission at gamma-ray wavelengths is not so the central SMBH. Hence, it would be a possible solution to set efficient. In terms of transparency, the near infrared region the power plants on a solid framework, something like struc- would be a possible wavelength. Stars rotating around the tures studied by Birch [9]. Some areas should be kept uncov- Galactic Centre are observed ([13], references therein), al- ered to yield emanating jets and accreting flows. though Sgr A* is still difficult to observe at infrared wave- lengths. This suggests that when we choose the transmission First, we estimate the distance where iron melts by radiation, frequency, we must take account of (1) the spectral energy assuming 1045 erg/s comes from a central point source. Given distribution of the radiation from the accretion disk, (2) energy this luminosity is generated by 10% of the Eddington luminos- conversion efficiency of the power plant for the transmission, 7 ity, the SMBH mass corresponds to 7 × 10 M~.