Research on SETI, black holes, XRB and star lifting

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This page is meant to stimulate SETI research on black holes, X-Ray binaries (XRB) and star lifting. It was initiated by Clément Vidal (2011). If you want to collaboratively edit it, you are welcome to Join EDU. You are welcome to email Clément Vidal to add more questions here, suggest corrections or solutions.


The Search for Extra-Terrestrials (SETI) has been unsuccessful so far. Additional new methods need to be taken into account, and, since we don't know anything about ETIs, it is wise to promote a variety of hypotheses and approaches.

General SETI strategies

The search for extraterrestrials can take three forms, searching for:

  • (1) ETs less advanced than us (e.g. finding bacteria on meteorites, trace of water, photosynthesis and other biosignatures)
  • (2) ETs at our level (e.g. the orthodox SETI of looking for intentional signals, Earth-like planets, etc.)
  • (3) ETs more advanced than us (e.g. astroengineering, Dyson spheres, star lifting operation, high energy use, high computational use, small scale and dense technologies -up to black hole technology-, X-Ray Binaries, cataclysmic variables, microquasars, etc.)

On this page, we focus on search strategies of the third kind (3).

Abbreviations used

  • ET: Extraterrestrial
  • ETI: Extra Terrestrial Intelligence
  • ERD: Energy Rate Density (Chaisson 2001, 2003)
  • BH: black hole
  • NS: neutron star
  • XRB: X-ray binary
  • LMXRB: Low mass X-ray binary
  • HMXRB: High mass X-ray binary
  • (WD/NS/BH)-(L/H)MXRB: (White Dwarf/Neutron Star/Black Hole) in a (Low/High)Mass XRB
  • (!): Speculative
  • (!!): Science-fiction like speculation

If references do not appear at the end of this page, they can be found in Vidal (2011).


Metrics - Energy Rate Density

Non-equilibrium systems, whether physical, biological or technological need to process an energy flow to sustain their activity (Nicolis and Prigogine 1977).

Eric Chaisson's metric (2001; 2003), the Energy Rate Density (ERD) is defined as the rate at which free energy transits in a complex system of a given mass. Its dimension is energy per time per mass (erg/s/g). This complexity metric is a very robust metric to describe 13 billion years of cosmic evolution. It may thus be helpful to provide indications of super civilizations ahead of us by 1-8 billion years. If the metric is indeed of universal validity, it should also apply to unknown extraterrestrial intelligence (ETI).

  • What is the highest Energy Rate Density (ERD) we can imagine in the universe?
    • What kind of system could achieve it?
    • Could we use this as an heuristic to search ETIs?
  • What are the highest ERD we can observe in the universe (outside Earth)?
    • Could we use this as an heuristic to search ETIs?
  • What is the ERD of accreting binaries?

If we take a dense star of 1.4 solar masses and 1.8 x 10^38 erg/s, (Frank et al. 2000, 205) we have an ERD equal to 6.4 x 10^4 erg/s/g. Another example is the fascinating SS433 system. If we take a luminosity of 10^40 erg/s, and a 10 solar masses black hole, we have an ERD of 5 x 10^5 erg/s/g (Data from Fabrika et al 2007).

Those values are extremely high for "natural" astrophysical systems. Indeed, a galaxy has an ERD of 0,5, a star 2. Accreting binaries are thus 4 to 5 orders of magnitude higher than galaxies or stars. Roughly, those binaries are respectively on the order of magnitude of a hunter-gatherer society, and of an industrial society. We might deal here with an exceptional and still natural regime. But maybe not. Accretion can be a stable phenomenon, which has for example not much in common with a very rapid, unstable and highly energetic supernova.

  • What are the ERD of accreting binary star systems?

How can we calculate it more precisely and systematically, using Eric Chaisson's (2001;2003) "energy rate density" metric?

Star Lifting

Here, we especially look at the possibility that ETIs have, are or will be engaging in star lifting. Consequences of such operations are likely to be observable.

  • Can we find evidence of star lifting?
    • See Martin Beech's (2008, 190-191) 12 possible signs of star lifting in operation.
    • (!) Exoplanets: Could some of them be in the process of being black-hole-formed?
      • Maybe the giant planets found near stars are put there artificially, to be NS- or BH-formed?
      • Observe their evolution!

    • Is it possible that a LMXB is created from a Sun-like star? Suggested by Beech (2008, 157)
  • What is the proportion of natural vs putative artificial binaries?

Consider our theoretical models or simulations of stellar evolution. Can we actually have simulations showing the proportion of binaries, their type, etc. assuming their natural physical properties and evolution? Does this fit with the real data? If not, could there be some star-lifting at play?

  • (!) Could some of observed binaries already display effects of star lifting?
    • Can we estimate the number of binary systems which form (1) with known mechanisms, versus (2) the number of binaries actually observed?
      • If there is a discrepancy between (1) and (2), could it be that some binary systems are artificial?
  • Search for civilizations failing star lifting
    • See Beech (2008, 154)
    • What catastrophes can we imagine?
  • Would a civilization want to lengthen or shorten the lifetime of stars?

It depends on what is the goal

    • to survive for a long time, with low energy (e.g. with a white dwarf) then it is advantageous to lengthen the star's lifetime.
    • for the purpose of using more rapidly the star's energy, then the star's lifetime is shortened. (!!) In that case, it should be sure to find another star afterwards! (see Migration)

Assessing XRB as ETIs

According to Vidal's (2011) reasoning, XRBs are good ETI candidate. How can we assess this hypothesis?

  • How can we distinguish a natural process from an artificial and unknown one?

Accretion is an ubiquitous astrophysical process in galaxy and planetary formation, so XRBs may simply always be natural. Let me however introduce an analogy. Fission can be found in natural forms, as well as fusion, which is one of the core energetic processes in stellar evolution. Yet, humans try to copy them, and would greatly benefit to -always- control them. So it is not because a process is known to be natural that its actual use is not driven by an intelligence. In fact, the situation may be even more subtle. The formation of XRBs might be natural, but controlled or taken over by ETIs, like a waterfall is a natural energy source humans can harness with dams. So, how can we develop criteria for natural versus artificial? Non-equilibrium thermodynamics, systems theory, artificial life, etc. because of their general concepts and applicability, will certainly provide key conceptual frameworks. Metrics like Freitas' (1984) sentience quotient or Chaisson's (2001, 2003) energy rate density are certainly very promising, and a KII-BΩ civilization should score high on them. Those metrics also indicate that the distinction natural versus artificial may be of a continuous nature.

  • Focusing on LMXRB

Mirabel et al. (2011) have suggested that BH-HMXRB play an important role in the early universe. It thus seems very unlikely that such BH-HMXRB are artificial, because life-as-we-know it wouldn't have had time to develop. It seems thus natural to focus SETI on LMXRB, which is also more consistent with research on star lifting.

  • Can we find evidence of control in the XRB's energy flow?

Energy flow regulation or control is a necessary condition for the growth, maintenance, evolution and reproduction of complex systems (see e.g. Aunger 2007; Chaisson 2011). Are some XRBs displaying such a feature?

  • Does the accretion process require fine-tuning?
    • Is a BH or NS easy or hard to stabilize in an accreting state, and to vary the accretion rate?

Narayan and Quataert (2005) suggest such fine-tuning, but it should be clarified and elaborated. See also Kalogera and Webbink (1996) in the context of neutron stars.

  • Can we find a black hole less than ~3 solar masses?

We can hypothesize that some accreting neutron stars are in fact artificial black holes. Indeed, the main observational technique to decide whether the very dense accreting object is a neutron star or a black hole is to estimate its mass. If the object has a mass superior to Chandrasekhar's limit of ~3 solar masses, it can only be a black hole. Otherwise, it is a neutron star. Therefore, the finding (by future methods) of a black hole less than ~3 solar masses may corroborate its artificial origin.

  • What is the effect of accretion of a small black hole on stars?
    • Could we detect such an effect?
  • Can we find planets harboring life orbiting accreting binaries?

Note that this assumes a biological and not postbiological civilization.

  • (!) Is there some useful work done by the dense accreting WD/NS/BH?

Can we use concepts inspired by dynamic energy budget or bioenergetics (e.g. energy balance) to assess if some of the energy in binaries might be used for the internal organization of the dense object? Note that this supposes to look at accreting binaries as complex systems. For example, in the case of black holes, they have a strong energy flow from the star to the accreting black hole; at irregular intervals, plasma jets are ejected at relativistic velocities, which may be interpreted as entropy production; and, the black hole may be a structurally and informationally rich entity, if we assume that it could be a technology like an ultimate computer (see Vidal 2011).

Migration of XRBs?

  • What is the origin, evolution, fate and possible migration of XRB?

With this question I mean that a compelling argument for the existence of advanced ETIs will most likely come from an evolutionary, statistical and global cosmic understanding of natural and possibly artificial stellar evolution in our and other galaxies.

  • Are there some binary systems which don't fit with binary stellar evolution?
    • Can we find binaries which were not formed during star formation?
  • How can binary systems move (e.g. XTE J1118+480; GRS 1915+105 and V404 Cyg) ?
  • Is there a mirgration of binaries to the galactic center?

See e.g. Muno et al. 2005; Mirabel 2011.

  • Are there less accreting LMXRB in younger galaxies?
    • If some binaries are indeed artificially produced, there should be less of them in young galaxies, and more in older galaxies. Is it the case?
    • Beware of observation selection effects, because farther away objects are more difficult to detect.

If they are below the boundary of the first possible intelligence-as-we-know-it, then it is a disproof of their intelligent origin. Karadashev (1997) summarized this approach by "the more distant, the less developed we expect".


Finding ETIs would be a revolution marking an end to "biocentrism", the idea that biology on Earth is unique in the universe. If postbiological ETIs are found, this would be an end to "intellicentrism", the idea that intelligence on Earth is unique in the universe.


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Beech, Martin. 2008. Rejuvenating the sun and avoiding other global catastrophes. Springer.

Chaisson, E. J. 2001. Cosmic Evolution: The Rise of Complexity in Nature. Harvard University Press.

———. 2003. “A Unifying Concept for Astrobiology.” International Journal of Astrobiology 2 (02): 91-101. .

———. 2011. “Energy rate density as a complexity metric and evolutionary driver.” Complexity 16 (3): 27-40. doi:10.1002/cplx.20323.

Dyson, F. J. 1966. The Search for Extraterrestrial Technology. In Perspectives in Modern Physics, ed. R.E. Marshak, 641–655. New York: John Wiley & Sons.

Fabrika, S. N., P. K. Abolmasov, and S. Karpov. 2006. “The supercritical accretion disk in SS 433 and ultraluminous X-ray sources.” Proceedings of the International Astronomical Union 2 (S238): 225–228.

Frank, Juhan, Andrew King, and Derek Raine. 2002. Accretion Power in Astrophysics. 3rd ed. Cambridge University Press.

Freitas, R. A. 1984. “Xenopsychology.” Analog Science Fiction/Science Fact 104: 41-53.

Kalogera, Vassiliki, and Ronald F. Webbink. 1996. “Formation of Low-Mass X-Ray Binaries. I. Constraints on Hydrogen-rich Donors at the Onset of the X-Ray Phase.” The Astrophysical Journal 458 (February 1): 301.

Kardashev, N.S. 1997. “Cosmology and Civilizations.” Astrophysics and Space Science 252 (1) (March 1): 25-40-40.

Mirabel, I. Felix. 2011. Stellar black holes: Cosmic history and feedback at the dawn of the universe. In Jets at all Scales, Proceedings of the International Astronomical Union, IAU Symposium, , 275:3-10. February 1.

Muno, M. P., E. Pfahl, F. K. Baganoff, W. N. Brandt, A. Ghez, J. Lu, and M. R. Morris. 2005. “An Overabundance of Transient X-Ray Binaries within 1 Parsec of the Galactic Center.” The Astrophysical Journal 622 (2): L113-L116. doi:10.1086/429721.

Narayan, Ramesh, and Eliot Quataert. 2005. “Black Hole Accretion.” Science 307 (5706) (January 7): 77 -80. doi:10.1126/science.1105746.

Nicolis, G., and I. Prigogine. 1977. Self-Organization in Nonequilibrium Systems: From Dissipative Structures to Order Through Fluctuations. Wiley, New York.

Vidal, C. 2011 Black Holes: Attractors for Intelligence? Presented at the Kavli Royal Society International Centre, "Towards a scientific and societal agenda on extra-terrestrial life", 4-5 Oct 2010.