IntroductionW? liv? in this incr?dibly vast univ?rs?, th? story go?s that, on? day back in th? 1940’s, a group of atomic sci?ntists, including th? famous Enrico F?rmi, w?r? sitting around talking, wh?n th? subj?ct turn?d to ?xtrat?rr?strial lif?. F?rmi is suppos?d to hav? th?n ask?d, “So? Wh?r? is ?v?rybody?” What h? m?ant was: If th?r? ar? all th?s? billions of plan?ts in th? univ?rs? that ar? capabl? of supporting lif?, and millions of int?llig?nt sp?ci?s out th?r?, th?n how com? non? has visit?d ?arth? This has com? to b? known as “Th? F?rmi Paradox”. F?rmi r?alis?d that any civilisation with a mod?st amount of rock?t t?chnology and an immod?st amount of imp?rial inc?ntiv? could rapidly colonis? th? ?ntir? Galaxy. Whil? int?rst?llar distanc?s ar? vast, p?rhaps too vast to b? conqu?r?d by living cr?atur?s with finit? lif?tim?s, it should b? possibl? for an advanc?d civilisation to construct s?lf-r?producing, autonomous robots to colonis? th? Galaxy. Th? id?a of s?lf-r?producing automaton was propos?d by math?matician John von N?umann in th? 1950’s. Th? id?a is that a d?vic? could; 1) p?rform tasks in th? r?al world and 2) mak? copi?s of its?lf (lik? bact?ria). Th? fast?st, and ch?ap?st, way to ?xplor? and l?arn about th? Galaxy is to construct Brac?w?ll-von N?umann prob?s. A Brac?w?ll-von N?umann prob? is simply a payload that is a s?lf-r?producing automaton with an int?llig?nt program (AI) and plans to build mor? of its?lf. Such a prob? could trav?l b?tw??n th? stars at a v?ry slow pac?. Wh?n it r?ach?s a targ?t syst?m, it finds suitabl? mat?rial (lik? ast?roids) and mak?s copi?s of its?lf.Growth of th? numb?r of prob?s would occur ?xpon?ntially and th? Galaxy could b? ?xplor?d in 4 million y?ars. Whil? this tim? span s??ms long compar?d to th? ag? of human civilisation, r?m?mb?r th? Galaxy is ov?r 10 billion y?ars old and any past ?xtrat?rr?strial civilisation could hav? ?xplor?d th? Galaxy 250 tim?s ov?r. Within a f?w million y?ars, ?v?ry star syst?m could b? brought und?r th? wing of ?mpir?. A f?w million y?ars may sound long, but in fact it’s quit? short compar?d with th? ag? of th? Galaxy, which is roughly t?n thousand million y?ars. Colonisation of th? Milky Way should b? a quick ?x?rcis?. This prompt?d F?rmi to ask what was an obvious qu?stion: “wh?r? is ?v?rybody?” If on? consid?rs th? amount of tim? th? Galaxy has b??n around (ov?r 10 billion y?ars) and th? sp??d of t?chnological advanc?m?nt in our own cultur?, th?n a mor? r?l?vant point is wh?r? ar? all th? sup?r-advanc?d ali?n civilisations.Kardash?v scal? – th? ?n?rg?tic incr?as?Russian astrophysicist, Nikolai Kardash?v propos?d a us?ful sch?m? to classify advanc?d civilisations. But looking around, h? didn’t s?? any cl?ar indication would poss?s on? of thr?? l?v?ls of t?chnology. A Typ? I civilisation similar to our own, on? that us?s th? ?n?rgy r?sourc?s of a plan?t. A Typ? II civilisation would us? th? ?n?rgy r?sourc?s of a star, such as a Dyson sph?r?. A Typ? III civilisation would ?mploy th? ?n?rgy r?sourc?s of an ?ntir? galaxy. A Typ? III civilisation would b? ?asy to d?t?ct, ?v?n at vast distanc?s. But w? hav? ?ncount?r?d nothing at all, so mayb? w?, us humans ar? at fault. “Tig?r got to hunt, bird got to fly; Man got to sit and wond?r ‘why, why, why?’ Tig?r got to sl??p, bird got to land; Man got to t?ll hims?lf h? und?rstand.” – Cat’s cradl?, Kurt Vonn?gut.Our civilisation us?s mor? and mor? ?n?rgy. ?n?rgy is all-purpos?, so w? don’t ?v?n n??d to und?rstand th? how or th? why of this ?n?rgy us? to s?? that this tr?nd is robust. ?xtrapolating this ?xpon?ntial incr?as? of ?n?rgy consumption, Kardash?v (1964) show?d that this would l?ad our civilisation to typ? KII in y?ar 5164 and to typ? KIII in 7764. Although Kardash?v’s original scal? is an ?n?rg?tic on?, it has oft?n b??n int?rpr?t?d as, and ?xtrapolat?d to a spatial on?. This is probably b?caus? th? ord?r of magnitud? of th? ?n?rgy proc?ss?d is as follows.Typ? KI harn?ss?s th? ?n?rgy of a Earth-lik? plan?t; typ? KII harn?ss?s th? ?n?rgy of a star and typ? KIII th? ?n?rgy of a galaxy. W? ar? curr?ntly a KI civilisation. L?t us ?xamin?, as a typical ?xampl?, our possibl? transition from typ? KI to typ? KII. What motivations could w? hav? to harn?ss th? ?n?rgy of th? Sun? Th?r? ar? ?ss?ntially two r?asons. First, simply to m??t our growing ?n?rgy consumption n??ds; s?cond, to avoid th? pr?dictabl? d?ath of our Sun, associat?d with th? d?struction of lif? on Earth. L?t us first consid?r how to m??t a civilisation’s growing ?n?rgy n??ds. Einst?in famously formulat?d th? matt?r-?n?rgy ?quival?nc? formula E=mc². If w? consid?r our solar syst?m, wh?r? can w? find most of its mass-?n?rgy? It is abov? all in th? Sun, sinc? 99.8% of our solar syst?m’s mass is in th? Sun. That is, 99.8% of th? ?n?rgy in our solar syst?m is to b? found in th? Sun. For any long-t?rm us?, th? Sun is thus th? obvious r?sourc? to harn?ss ?n?rgy from.Exploiting th? ?n?rgy of a star is an ?xplorativ? ?ngin??ring fi?ld known as star lifting, also call?d st?llar mining, st?llar ?ngin??ring or ast?ro-?ngin??ring (s?? R??v?s 1985; Crisw?ll 1985; B??ch 2008). Th? s?cond inc?ntiv? to ?ngin??r our Sun is to avoid its r?d giant phas? which will b?gin in about 5 billion y?ars. This ?nt?rpris? is vital if w? ar? conc?rn?d by saving lif? on Earth. Various proc?ss?s hav? b??n propos?d for this purpos?, r?sulting in an ?limination of this r?d giant phas?. Th? topic is tr?at?d ?xt?nsiv?ly by Martin B??ch (20083). From a SETI p?rsp?ctiv?, this l?ads to concr?t? and obs?rvabl? pr?dictions. B??ch (2008, 190-1913) propos?s 12 possibl? signs of st?llar r?juv?nation in progr?ss.Dokucha?v has also said, “Th? nak?d c?ntral singularity illuminat?s th? orbiting int?rnal plan?ts and provid?s th? ?n?rgy supply for lif? supporting,” h? adds. “Som? additional highlighting during th? night tim? com?s from ?t?rnally circulating photons.” So any civilisation capabl? of doing so, which would probably rank as a typ? III advanc?d civilisations on th? Kardash?v scal?, would d?riv? light and h?at from orbiting photons and ?n?rgy from within th? singularity its?lf. Mor? int?r?stingly, such a civilisation would b? compl?t?ly clos?d off to th? r?st of th? univ?rs? b?yond th? ?v?nt horison, just as w? too, can not s?? anything insid? of.Barrow scal? – th? inward manipulationJohn Barrow (1998) classifi?d t?chnological civilisations by th?ir ability to control small?r and small?r ?ntities. This tr?nd l?ads to major soci?tal r?volutions. Biot?chnology, nanot?chnology and information t?chnologi?s ar? progr?ssing at an acc?l?rating pac? and all st?m from our abiliti?s to control and manipulat? small scal?s ?ntiti?s. This pivotal and ov?rwh?lming tr?nd toward small spatial scal?s is larg?ly ov?rlook?d in SETI, r?sulting in th? Barrow scal? b?ing not w?ll-known. Barrow ?stimat?s that w? ar? curr?ntly a BIV civilisation which has just ?nt?r?d nanot?chnology. Anoth?r argum?nt for th? importanc? of th? Barrow scal? is that, from th? r?lativ? human point of vi?w, th?r? is mor? to ?xplor? in small scal?s than in larg? scal?s.As count?r-intuitiv? as it is, spac? ?xploration off?rs mor? prosp?ct in small scal?s than in larg? scal?s. That humans ar? not in th? c?nt?r of th? univ?rs? is also tru? in t?rms of scal?s. This impli?s that th?r? is mor? to ?xplor? in small scal?s than in larg? scal?s. Richard F?ynman (1960) popularis?d this insight wh?n h? said “th?r? is pl?nty of room at th? bottom”. In contrast with larg? cosmological scal?s, manufacturing, t?sting, ?xploring and ?xploiting small scal? t?chnologi?s is ?asi?r, ch?ap?r and mor? controllabl?. It is also mor? ?ffici?nt ?n?rg?tically.Sinc? th? d?v?lopm?nt of such t?chnologi?s is not hamp?r?d by th? finit?n?ss of th? sp??d of light, its acc?l?rating progr?ss has no r?ason to slow down until w? r?ach th? Planck scal?. Futurist and syst?ms th?orist John Smart (2009) charact?ris?d this tr?nd as Spac?-Tim?-En?rgy-Matt?r (STEM) ?ffici?ncy and d?nsity, or “STEM Compr?ssion”. It can also simply b? summaris?d with th? motto of “doing mor? with l?ss”.Black hol?s as attractors for int?llig?nc?If w? tak? s?riously th? Barrow scal?, w? do not ?v?n n??d to sp?culat? on any particular black hol? t?chnology. W? can simply assum? that an int?llig?nt civilisation will d?v?lop to typ? B?, what?v?r its purpos? is in using black hol?s. Th? r?ad?r av?rs? to sci?ntific and philosophical sp?culation might thus jump dir?ctly to s?ction 3 for an application of th? two-dim?nsional m?tric. How?v?r, black hol?s ar? fascinating attractors, not only b?caus? of th?ir stagg?ring gravitational fi?ld, but also b?caus? th?y ar? an int?llig?nc?’s gr?at?st pot?ntial. L?t us s?? why with a short adv?ntur? on th? sp?culativ? topic of black hol? t?chnology.Black hol?s ar? th? d?ns?st obj?cts in th? univ?rs?. If w? want to fac? th? n??ds of consuming mor? ?n?rgy, it might b? b?n?ficial to stor? or ?xtract ?n?rgy from black hol?s. Rog?r P?nros? (1969, 270-272) imagin?d th? following ?xtraction m?chanism. It consists of inj?cting matt?r into a black hol? in a car?fully chos?n way, th?r?by ?xtracting its rotational ?n?rgy (Misn?r, Thorn?, and Wh??l?r 1973, 908). Blandford and snaj?k (1977) sugg?st?d a similar proc?ss with ?l?ctrically charg?d and rotating black hol?s. Oth?r proposals sugg?st coll?cting ?n?rgy from gravitational wav?s of colliding black hol?s. Misn?r imagin?d this in 1968 as a p?rsonal communication to P?nros? (19696). Frautschi (1982) also propos?d to m?rg? black hol?s as a way to produc? a pow?r sourc?.Which oth?r soci?tal functions could black hol?s fulfill? Louis Cran? (2010, 370) has sugg?st?d that black hol?s ar? th? p?rf?ct wast?-disposal, although th?y should b? manipulat?d with gr?at car?. H? has also conduct?d an ?xt?nsiv? study with W?stmor?land on th? possibility of black hol? starships (Cran? and W?stmor?land 2009). Furth?rmor?, g?n?ral r?lativity l?ads to th? fascinating topic of tim? trav?l via worm hol?s, th?or?tical cousins of black hol?s. Although no ?vid?nc? of th?ir ?xist?nc? is availabl?, th?y could in th?ory provid? shortcuts for trav?ling in spac?tim? (for popular accounts s?? Thorn? 1994; Randall 2005).L?t us assum? that t?rr?strial and ETIs ar? curious and continu? to d?v?lop sci?nc?. Black hol?s, ?sp?cially th?ir int?riors, curr?ntly chall?ng? our knowl?dg? of th? thr?? fundam?ntal physical th?ori?s: quantum m?chanics, g?n?ral r?lativity and th?rmodynamics. For sci?ntific purpos?s, th?r? might b? an inc?ntiv? to artificially produc? black hol?s to b?tt?r und?rstand th?m. Ind??d, sinc? th? 80’s sci?ntists hav? consid?r?d th? possibility of making “univ?rs?s in th? lab” (Ansoldi and Gu?nd?lman 2006 for a r?vi?w). Although improbabl? sourc?s of dang?r, som? conc?rns hav? b??n rais?d r?garding th? accid?ntal production of micro black hol?s in particl? acc?l?rators (Giddings and Thomas 2002). Still, w? might want to produc? th?m int?ntionally in th? futur?. A mor? concr?t? sci?ntific application of black hol? t?chnology is to us? th?m as t?l?scop?s or communication d?vic?s.How is it possibl?? An ?stablish?d cons?qu?nc? of g?n?ral r?lativity th?ory is that light is b?nd?d by massiv? obj?cts. This is known as gravitational l?nsing. For a f?w d?cad?s, r?s?arch?rs hav? propos?d to us? th? Sun as a gravitational l?ns. At 22.45AU and 29.59AU w? hav? a focus for gravitational wav?s and n?utrinos. Starting from 550AU, ?l?ctromagn?tic wav?s conv?rg?. Thos? focus r?gions off?r on? of th? gr?at?st opportunity for astronomy and astrophysics, off?ring gains from 2 to 9 ord?rs of magnitud? compar?d to Earth-bas?d t?l?scop?s. Ov?r th? y?ars, Claudio Maccon? (2009) has d?taill?d with gr?at t?chnical pr?cision such a sci?ntific mission, call?d FOCAL. It is also worth noting that such gravitational l?nsing could also b? us?d for communication.If w? want to continu? and improv? our qu?st for und?rstanding th? cosmos, this mission is a gr?at opportunity to compl?t? our fussy astronomy with a focus?d on?. In oth?r words, th? tim? may b? rip? to put on our cosmic glass?s. But oth?r ETIs may alr?ady hav? binoculars. Ind??d, it is ?asy to ?xtrapolat? th? maximal capacity of gravitational l?nsing using, inst?ad of th? Sun, a much mor? massiv? obj?ct, i.?. a n?utron star or a black hol?. This would probably consitut? th? most pow?rful possibl? t?l?scop?. This possibility was ?nvision?d — y?t not d?v?lop?dby Von Eshl?man in (1991). Sinc? obj?cts obs?rv?d by gravitational l?nsing must b? align?d, w? can imagin? an additional dilating and contracting focal sph?r? or artificial swarm around a black hol?, th?r?by obs?rving th? univ?rs? in all dir?ctions and d?pths. Mayb? such focal sph?r?s ar? alr?ady in op?ration.What is th? maximal information that can b? proc?ss?d by an advanc?d ETI? Visionary sci?ntist Rob?rt A. Fr?itas (1984) introduc?d th? s?nti?nc? quoti?nt, which is a “scal? of cosmic s?nti?nc? univ?rsally applicabl? to any int?llig?nt ?ntity in th? cosmos”. At its limits, w? hav? th? maximal computational d?nsity of matt?r, what S?th Lloyd (2000) mor? r?c?ntly call?d th? “ultimat? comput?r”. What do?s such a comput?r look lik?? Lloyd argu?s that it is a black hol?. Int?r?stingly, if Moor?’s law is ?xtrapolat?d, w? attain such a maximal computational pow?r by 2205 (Lloyd 2005, 162). But black hol?s can b? ?v?n mor? than ultimat? comput?rs. At th? ?dg? of th?or?tical comput?r sci?nc?, som? mod?ls of computation outp?rform Turing’s original d?finition. Such d?vic?s ar? call?d hyp?rcomput?rs (Earman and Norton 1993). Th?y ar? th?or?tically possibl? assuming particular spac?-tim? structur?s or with slowly rotating black hol?s (s?? Et?si and I N?m?ti 2002; Andr?ka, I N?m?ti, and P N?m?ti 2009). If th? construction of such hyp?rcomput?rs is succ?ssful and ind??d possibl?, this would bring qualitativ?ly n?w ways to und?rstand and mod?l our univ?rs?. A br?akthrough p?rhaps comparabl? to th? inv?ntion of our ubiquitous computing machin?s.Int?llig?nc? is th? capacity to solv? probl?ms. It is by focusing on univ?rsal and longt?rm probl?ms that w? hav? th? high?st chanc?s to und?rstand th? purpos? of pr?sum?d ETIs. I s?? only two such s?rious probl?ms. Th? first is th? alr?ady m?ntion?d r?d giant phas? capabl? of wiping out lif? in a solar syst?m lik? ours. This is a fundam?ntal chall?ng? any civilisation born on th? shor? of a Sun-lik? star will hav? to fac?. A promising SETI strat?gy is thus to s?arch for civilisations r?fusing this fat?, by looking at artificially modifi?d stars. According to Crisw?ll (1985, 832) star lifting can consid?rably ?xt?nd a civilisation’s tim? with matt?r to ?n?rgy conv?rsion, up to 2 millions tim?s th? pr?s?nt ag? of th? univ?rs?, assuming th? civilisation stays at KI. Y?t, ?v?n this runs out in th? long t?rm b?caus? th? star will ultimat?ly run out of usabl? ?n?rgy.What is th? n?xt l?v?l? Possibly migration, but that also cannot continu? for?v?r, b?caus? n?w star formation com?s to an ?nd in th? v?ry long t?rm (Adams and Laughlin 1997). Aft?r r?alising that th? fat? of stars is doom?d, th? long?st t?rm and truly univ?rsal probl?m is th? continuation of th? univ?rs? as a whol?, to avoid its in?vitabl? global ?ntropy incr?as? and d?ath (?irkovi? 2003 on physical ?schatology). Th? s?cond chall?ng? is thus, “How can w? mak? lif?, int?llig?nc? and ?volution surviv? ind?finit?ly?” Answ?ring this qu?stion is of cours? b?yond th? scop? of this pap?r, but l?t us m?ntion two proposals which includ? a rol? for black hol?s. Fr??man Dyson propos?d in his landmark (1979) pap?r that a civilisation could hib?rnat? and ?xploit th? tim? dilation ?ff?cts n?ar black hol?s, to surviv? for?v?r. This is utilising th? id?a, of cons?rving ?n?rgy in th? b?st possibl? way, which would m?an that this int?llig?nt lif? no long?r r?quir?s th? primitiv? id?a of “conqu?ring” stars, galaxi?s, ?ntir? univ?rs?s, ?tc. which is not sustainabl? at all. How?v?r, this sc?nario do?sn’t work if th? univ?rs? continu?s its acc?l?rat?d ?xpansion (Dyson 2004, xv). Y?t, th? cor? of th? argum?nt can b? maintain?d if w? r?plac? digital comput?rs by analog on?s (Dyson 2007).Anoth?r sp?culativ? solution is to r?produc? th? univ?rs? (Harrison 1995; Gardn?r 2003; Balás 2005; Smart 20095; Gribbin 2009; St?wart 2010). This sc?nario combin?s th? origin and futur? of th? univ?rs? with a rol? for int?llig?nt lif?. I hav? call?d it Cosmological Artificial S?l?ction (s?? Vidal 2008, 2010; Vaas 2010, 2011 for criticism; and Vidal 2011 for a r?spons?) as it is a philosophical ?xt?nsion of Smolin’s (1992, 1997) th?ory of Cosmological Natural S?l?ction. It is also worth noting that th? futur? disciplin? of Artificial Cosmog?n?sis (Vidal 200834), analogous to Artificial Lif? but ?xt?nd?d to th? cosmos, would b?n?fit th? pow?r of ultimat? comput?rs, to run simulations of whol? univ?rs?s. Finally, if w? assum? that our univ?rs? is a black hol? (Pathria 1972), th? pussling fin?-tuning of univ?rsal constants could its?lf b? int?rpr?t?d as an int?llig?nt signal from pr?vious univ?rs? mak?rs (Pag?ls 1989, 155-156; Gardn?r 200330). This is a radical proposal and th? “S?arch for Extra Univ?rsal Int?llig?nc?” fi?ld has y?t to ?m?rg?.Black hol? star liftingIn a SETI minds?t, consid?ring s?riously that black hol?s ar? attractors for int?llig?nc?, w? can now start to ask th? following qu?stions. What ar? th? obs?rvabl? manif?stations of a black hol? wh?n it’s us?d as an ?n?rgy sourc?? as wast? disposal? as a tim?-machin?? as a starship ?ngin?? as an ultimat? or hyp?r comput?r? as a univ?rs? production facility? Th? ?x?rcis? is highly sp?culativ?, and rais?s th? ?ffici?ncy obj?ction. W? saw that th? Barrow scal? tr?nd mak?s civilisations d?v?lop with mor? and mor? ?ffici?ncy. This would mak? small black hol?s mor? us?ful and thus hard or impossibl? to d?t?ct. It would b? lik? trying to d?t?ct from Earth th? ?xist?nc? of nanot?chnology on th? Moon.This is th? ?ss?nc? of Smart’s (20095) r?spons? to F?rmi’s paradox. W? don’t s?? oth?r ETIs b?caus? th?y ar? confin?d insid? black hol?s. How?v?r, th? two tr?nds of mor? ?n?rgy us? and mor? ?n?rgy ?ffici?ncy n??d not b? incompatibl?. Roughly sp?aking, our civilisation has always b??n mor? ?ffici?nt y?t always using incr?asing amounts of ?n?rgy. Th? k?y li?s in th? availability of ?n?rgy. If it is poor, ?ffici?ncy will strongly constrain civilisation d?v?lopm?nt. If ?n?rgy is larg?ly availabl?, th?n ?ffici?ncy matt?rs l?ss and civilisations can also grow on th? Kardash?v scal?. In his s?minal pap?r, Dyson (1966, 643) assum?d that ETIs would us? t?chnology w? can und?rstand.H? qualifi?d this assumption as “totally unr?alistic”. How?v?r, th?r? is a profound dil?mma h?r?. If w? r?sp?ct this rul?, w? r?strict our s?arch to civilisations roughly at our d?v?lopm?ntal l?v?l, not r?ally high?r. Th? s?arch for ETIs mor? advanc?d than us is unlik?ly to succ??d. But if w? r?l?as? this rul?, this brings a paradox. It will b? hard, if not impossibl?, to argu? that a ph?nom?non w? don’t und?rstand is artificial, sinc? its t?chnology will, by d?finition, b? ali?n to us.Signs of KII-B? civilisationsW? don’t n??d to imagin? or to wait b?caus? such configurations alr?ady ?xist. Ind??d, 18 syst?ms compos?d of a black hol? accr?ting gas from a star hav? b??n found today (?.g. GRO J1655-40, 1659-487, GRS 1915+105, SS433, ?tc.). Th?y ar? part of th? family of binary syst?ms, call?d X-Ray Binari?s (XRB) b?caus? of th?ir ?missions in th? X-Ray ?l?ctromagn?tic sp?ctrum. Sinc? a f?w d?cad?s, th?y ar? activ?ly studi?d as natural -though som?tim?s intriguing- astrophysical syst?ms. Importantly, r?s?arch?rs hav? conclud?d that a thin accr?tion disk around a rotating black hol? is th? most ?ffici?nt pow?r sourc? in th? univ?rs? , a proc?ss up to 50 tim?s mor? ?ffici?nt than nucl?ar fusion occurring in stars (Thorn? 1974; Narayan and Quata?rt 2005).If any civilisation is to climb th? Kardash?v scal?, it would c?rtainly at som? point want to mast?r that ?n?rg?tic sourc?. W? call such an ?nd?avor black hol? star lifting. L?t us call such an hypoth?tical civilisation KII-B?. It is of Typ? II on Kardash?v’s scal?, b?caus? it is abl? to harn?ss th? ?n?rgy of a star; and typ? ? on Barrow’s scal?, sinc? it manipulat?s spac?-tim?’s structur? with black hol? t?chnology. In fact, som? XRB ?v?n display th? main f?atur?s of non-?quilibrium syst?ms. Th?y hav? a strong ?n?rgy flow from th? star to th? accr?ting black hol?; at irr?gular int?rvals, plasma j?ts ar? ?j?ct?d at r?lativistic v?lociti?s, which may b? int?rpr?t?d as ?ntropy production; and, th? black hol? may b? a structurally and informationally rich ?ntity, if w? assum? that it could b? a t?chnology lik? an ultimat? comput?r. W? also can not? that th? black hol? is not primarily us?d as an ?n?rgy sourc?, but as a t?chnology which n??ds ?n?rgy.Accr?ting binari?s ar? found in a gr?at vari?ty of configurations. Our two-dim?nsional m?tric allows to also sp?culat? on th? ?xist?nc? of oth?r l?ss advanc?d civilisations than KII-B?. A young typ? KII might b? accr?ting th? ?n?rgy from a whit? dwarf star, which is nothing ?ls? than a burnt-out Sun-lik? star. A mor? matur? KII may b? using a n?utron star accr?ting syst?m. W? can also hypoth?sis? that som? accr?ting n?utron stars ar? in fact artificial black hol?s. Th? main obs?rvational t?chniqu? to d?cid? wh?th?r th? v?ry d?ns? accr?ting obj?ct is a n?utron star or a black hol? is to ?stimat? its mass. If th? obj?ct has a mass sup?rior to Chandras?khar’s limit of 3 solar mass?s, it can only b? a black hol?. Oth?rwis?, it is a n?utron star.Th?r?for?, th? finding (by futur? m?thods) of a black hol? l?ss than 3 solar mass?s may corroborat? its artificial origin. What about mor? than KII? Th? Chandra X-Ray spatial t?l?scop? provid?d data showing that Low-Mass XRB (LMXB) ar? ov?rabundant within 1 pars?c of th? galactic c?nt?r (Muno ?t al. 2005). Could th?s? b? civilisations migrating toward th? sup?rmassiv? black hol?? Although it sounds lik? a sci?nc?-fiction nov?l, Vyach?slav I. Dokucha?v (2011) r?c?ntly sugg?st?d that stabl? p?riodic orbits ar? th?or?tically possibl? insid? sup?rmassiv? black hol?s, and th?r?for?, may b? habitabl?. Frank Tipl?r (1997) also ?nvision?d with gr?at d?tails th? possibility of a K? civilisation mast?ring hug? computational capacity.