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High Energy Astrobiology

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The Beginning and the End

Part of the book series: The Frontiers Collection ((FRONTCOLL))

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This chapter proposes a new concrete hypothesis to search for and assess the existence of advanced extraterrestrial life. We first point out two methodological fallacies that we call naturality of the gaps and artificiality of the gaps and propose a more balanced astrobiological stance. We point out many limiting and implicit assumptions in SETI, in order to propose a “Zen SETI” that opens up the search space. In particular, we outline the case for postbiological evolution, or the probable transition from a biological paradigm to a nonbiological paradigm. We then discuss criteria to distinguish natural from artificial phenomena. We start with global criteria (strangeness heuristic, non-exclusiveness heuristic, equilibrium heuristic, and inverse distance-development principle); go on to thermodynamic criteria (thermodynamic disequilibrium and energy flow control); and finally present living systems criteria (Miller’s 19 critical functional subsystems). Then we introduce a two-dimensional metric for civilizational development, using the Kardashev scale of energy consumption increase and the Barrow scale of inward manipulation. To support Barrow’s scale limit, we present energetic, societal, scientific, computational, and philosophical arguments that black holes are attractors for intelligence. Taken together, these two civilizational development trends lead to an argument that some existing binary stars may actually be advanced extraterrestrial beings. Since those putative beings actively feed on stars, we call them starivores. We elaborate another independent thermodynamic argument for their existence, with a metabolic interpretation of some binary stars in accretion. We further substantiate the hypothesis with a tentative living systems interpretation. Ten critical living subsystems are suggested to apply to interacting binaries composed of a primary white dwarf, neutron star, or black hole. We critically discuss the hypothesis by formulating and replying to ten objections. The question of artificiality remains open, but I propose concrete research proposals and a prize to continue and further motivate the scientific assessment of this hypothesis.

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  1. 1.

    Dick calls biocentrism the “extraterrestrial/biophysical” worldview. It asserts simply that life on Earth is unique in the universe, and is not the view or belief that the rights and needs of humans are no more important than those of other living things.

  2. 2.

    This is a pun in French. Literally it means “black holes are troubling”; but in French, “troublant” (troubling) has the same pronunciation as “trou blanc”, which means “white hole”.

  3. 3.

    Other neologisms could have been stellivore (from Latin stella, star; and vorus, eater) or asterophage (from Greek astero, star; and phage, eater). But I prefer "starivore" (from English "star" with Latin vorus) for its ease of understanding, probably because of its proximity to "carnivore".

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Correspondence to Clément Vidal .

Open Questions

Open Questions

1.1 A High Energy Astrobiology Agenda: The Starivore Hypothesis

Current research in astrobiology focuses on searching for extraterrestrial life that is less advanced than us, such as bacteria or traces of a biosphere in an exoplanet. This makes sense, because these are features of life on Earth that we know and that we know how to recognize. A naive symmetry argument would suggest we divide our resources in two, and use one half to search for less advanced extraterrestrials and the other half for more advanced ETI. But even that is not enough, since we saw that ETI may be on average 2 billion years older than us. So it would actually make sense to spend much more in the search for advanced extraterrestrials.

The works of Dyson (1960) and Kardashev (1964) advanced the idea that advanced extraterrestrials use much more energy than us. This is the assumption of high energy astrobiology . The starivore hypothesis invites us to look back at high energy astrophysics with a fresh astrobiological perspective. We already encountered many open questions to test the hypothesis. Let us now summarize and specify them to propose a high energy astrobiological agenda.

Many ideas in this chapter are necessarily highly speculative, for how else could we approach a search for hypothetical ETI over a billion years more advanced? Yet the hypothesis that some binary systems in accretion are ETIs is testable. We have plenty of data about binaries, and we can gather more. This is to be contrasted with other proposals, such as Dyson spheres or Bracewell probes, which so far have no observational counterpart.

What is the ideal profile of the high energy astrobiologist? She is not swayed by prejudices regarding artificiality or naturality of the gaps. Instead, she takes a more careful astrobiological stance. She understands high energy astrophysics models and theories. But she spends equal time with artificial and natural models to tackle the so far poorly understood high energy phenomena in the cosmos. Furthermore, her knowledge and interests extend to systems theory, living systems theory, and the sciences of complexity. Other research interests may include biology and ecology, especially general biological laws, and the field of energetics. Experts in energetics would be able to take a fresh look at energy exchanges in binaries from a more biologically inspired perspective.

1.2 General Agenda

Let us summarize the specific predictions regarding putative starivores:

  • Discovery of a black hole of less than 3 solar masses. In astrophysics, stellar black holes are the result of gravitational collapse of a massive star. If the remnant exceeds the Tolman–Oppenheimer–Volkoff limit (3–4 solar masses), it will implode in a black hole. Finding a black hole of less than 3 solar masses would thus mean that the black hole formation took another road, possibly an artificial one.

  • Low-rate planetary accretion.

  • An instance of migration, where the motion of a dense body (WD/NS/BH) navigating in the galaxy is not random but directed toward the nearest star.

Another project is to continue to develop criteria for artificiality. Our list does not pretend to be exhaustive, and much more work is required to resolve this question. We saw that informational criteria are demanded if we want to test whether or not there is a message in pulsars. Even an excellent criteria list will not be enough to convincingly prove the existence of extraterrestrials. What we need are alternative models leading to different predictions. But what motivation would we have to build alternative models in addition the natural models we already have?

The strongest motivation comes from showing the limitations, contradictions, unsolved problems, or shortcomings of existing astrophysical models of binaries. Then we can propose alternative high energy astrobiological models that not only solve those problems but also lead to new and different predictions. Astrophysical or astrobiological models leading to the most successful predictions will find increasing favor. Although I am no expert in binary astrophysics, let me mention a few further open issues in the field and then propose more precise research proposals to test the starivore hypothesis from an astrobiological stance.

We saw that nova ejecta display heavy element abundances. It remains a difficult scientific challenge to explain the enrichment mechanism (see Prialnik 2001).

In binaries with accretion discs, the origin of disc viscosity remains highly uncertain. As Hellier (2001, p. 59) writes:

Although viscosity is essential to the operation of an accretion disc, the physical origin of the viscosity has been uncertain, defying theoretical investigation for many years. We know that molecules are sticky, attempting to form chemical bonds with their neighbours (this accounts for the viscosity of everyday materials such as treacle); however, discs are so diffuse that molecular viscosity is too feeble by a factor of a billion to explain their behaviour.

Recurrent novas usually flare after a brightening due to an excess in accretion, and their luminosity fades after the outburst. But as in the biological world, the binary world is full of exceptions. In his impressive review of recurrent novas, Schaeffer (2010) drew attention to a fading that occurred before the outburst:

Why did T CrB suffer a distinct, significant, and unique fading in the year before its 1946 eruption? And why would this fading behavior be different in the B and V bands? The fading is by around one magnitude below the usual level of the system, with this going to two magnitudes below the usual level in the B-band at a time 29 days before the eruption. My first thought is that the accretion turned off (for unknown reason) hence making the system lose the light from the accretion disk, but maybe the depth of the drop will require the red giant companion to be dimmed somehow. And what is the physical connection between this fading and the subsequent nova eruption? That is, how can the turning off of accretion anticipate or trigger the nova event?

Let us return to a possible extragalactic SETI. If there is a developmental pattern in civilizations, we should see ever fewer binary systems in accretion as we look deeper into space at stars in ever younger galaxies. Do we in fact? This is an application of the inverse distance-development principle.

For example, what about extragalactic pulsars? The starivore hypothesis predicts that they should be very rare. Such pulsars would be detectable, because many pulsars display giant pulses (see McLaughlin and Cordes 2003). Are they rare? The search for extragalactic pulsars is still in its infancy, yet out of 1,500 radio pulsars known, only about 25 are extragalactic, all located in the nearby dwarf galaxies of the Magellanic Clouds (McLaughlin and Cordes 2003, p. 983).

If density is an indicator of development, one prediction is that the proportion of accreting WD/NS/BH decreases as we look at more distant galaxies. Is this so?

Are we ready to contact starivores? If we take the starivore hypothesis seriously, communication with extraterrestrial intelligence (CETI) can raise its chance of succeeding by targeting binary systems. Of course, huge ethical issues need to be discussed before sending a signal to such highly advanced putative civilizations. Humanity should assess the risk–benefit tradeoff. The maximum risk is their coming and destroying the Earth or the Sun. The maximum benefit is that they collaborate fully with us, for example initiating us into the cosmic mysteries, and boosting our evolutionary development incredibly thanks to their technology, knowledge, and wisdom.

1.3 Research Proposals

Let us now turn to more concrete research proposals. Some of my readers may think that it is easy and fun to speculate, but that we have done more science fiction than science. They are partly right, and this is why it is essential to conduct new research with actual data on binaries to assess their naturality or artificiality.

Below are the seeds of four scientific research proposals which, if successful, will corroborate the existence of starivores. But only the last one promises to give indisputable proof of extraterrestrial intelligence.

1.3.1 Gamma-Ray Bursts and Binaries

Are starivores protected from gamma-ray bursts? Such events are unusually violent, and a galactic gamma-ray burst could wipe out eukaryotes at a range of 14 kpc from the explosion (see Scalo and Wheeler 2002; and also Ćirković et al. 2009). Long-lived civilizations would certainly anticipate such rare but possible catastrophes. We should be able to show either that binaries are strongly disturbed, dislocated, or destroyed by gamma ray bursts (which would tend to falsify the starivore hypothesis) or that they are suprisingly robust to such disturbances (which would tend to corroborate the starivore hypothesis).

1.3.2 Kleiber’s Law and Semi-Detached Binaries

When we analyzed binaries with living system theory, or when we applied a scaling law of reproduction time to black holes, we applied biological concepts and theories to astrophysical systems. This is indeed part of a general biological (or evolutionary developmental) view of the universe. It remains a challenge for future generations to assess whether this view is correct. As Dick (1996, pp. 1–2) writes,

The whole thrust of physical science since the seventeenth-century scientific revolution has been to demonstrate the role of physical law in the universe, a mission admirably carried out by Kepler, Galileo, Newton, and their successors. The question at stake in the extraterrestrial-life debate is whether an analogous “biological law” reigns throughout the universe.

What other robust biological laws could be applied to binaries? Kleiber’s law (Kleiber 1932) is the observation that in living organisms the metabolic rate scales to the ¾ power of their mass. It is remarkable, because it holds over 16 orders of magnitude—although the scaling exponent changes slightly (see DeLong et al. 2010 for a recent review). This validity across so many scales suggests that it could hold even for macroscopic living systems, such as cities (Isalgue et al. 2007) or putative starivores. This law is illustrated in Fig. 9.14.

Fig. 9.14
figure 14

Relationship between whole organism metabolic rate and body mass for heterotrophic prokaryotes, protists, and metazoans plotted on logarithmic axes (DeLong et al. 2010, p. 12942)

Does this law apply to transient accreting binaries? The hypothesis is that if binaries are starivores, they should conform to this law. If not, it is less likely. How can we test this? It is easy. We need to gather the relevant data for binaries. We can simply interpret the accretion rate as a metabolic rate (both are energy flow metrics) and plot the mass of the primary on the x-axis. Kepler’s law famously applies to planets, but does Kleiber’s law apply to binaries?

This research program could also be coupled with a systematic calculation of the free energy rate density complexity metric proposed by Chaisson. The only additional parameter to take into consideration is the age of the system.

1.3.3 Scale Relativity and Binaries

Scale relativity (see e.g. Nottale 2011) generates probability distributions for the formation of gravitational structures. It gives probabilities to obtain single, double, triple, or n-body systems. Preliminary results explain why pairs of galaxies are so common (Nottale 2011, pp. 654–658).

This project consists in applying scale relativity to the formation of binary systems. If binaries are starivores, the prediction of scale relativity should fail. In particular, we should observe more binary systems than would result from natural gravitational formation. Or there should be proportionally fewer pairs of galaxies than binary systems. However, the picture could be more complicated if putative starivores migrate and leave single depleted stars.

Furthermore, applying the inverse distance-development principle, ever more remote galaxies should fit ever more closely the predictions of scale relativity. Of course, this project represents a lot of work, but it is a global approach which, even if it ends up dismissing the starivore hypothesis, would teach us a lot about star formation.

If the project succeeded, we could obtain an estimate of the number of intelligent civilizations in the galaxy simply by subtracting the observed number of binaries from the predicted number.

1.3.4 Pulsars Decoding

Finally and most importantly, a convincing proof of ETI should include information processing. This is why I insisted that the assessment of whether there are messages in pulsars should be a priority (see Sect. 9.4.6). Decoding an extraterrestrial message will certainly be an amazingly difficult task. But a first easier step is to assess whether pulses display informational complexity. This can be evaluated using Kolmogorov complexity (e.g. Li and Vitányi 1997) or logical depth (Bennett 1988a, b). Pulsars signals could be benchmarked against natural signals (e.g. sea waves) and artificial signals (e.g. wi-fi). If they scored like sea waves, they would more likely be natural; if they scored like a wi-fi signal, they would more likely be artificial.

1.4 The High Energy Astrobiology Prize

After examination by a scientific jury, the Evo Devo Universe (EDU) community will be happy to award a 500 euro High Energy Astrobiology Prize for the first peer-reviewed paper on any of these projects (gamma-ray bursts and binaries, Kleiber’s law, scale relativity and binaries, assessing or decoding the informational complexity of pulsar pulses). The prize will of course be awarded for either a positive or a negative result. New research proposals to test all the ways there could be intelligence in interacting binaries are also most welcome. If you would like to contribute but do not have the scientific expertise to do so, we welcome donations to make the high energy astrobiology prize even more attractive. For more details, visit:

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Vidal, C. (2014). High Energy Astrobiology. In: The Beginning and the End. The Frontiers Collection. Springer, Cham.

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