The scientific search for intelligent life in outer space represents one of the most compelling quests that humanity has ever undertaken. In recent years, astronomers have discovered large numbers of exoplanetary systems, and if one entertains the notion that intelligent life may not be unique to our planet, the Search for Extra-Terrestrial Intelligence (SETI) would seem like a promising endeavour. However, astronomers have now been scanning the skies for more than 50 years, without detecting any communication signals from alien civilizations. While signal-based searches should certainly continue as new and better telescopes (like the Square Kilometer Array) come on line, alternative strategies should also be considered.
What if the nearest extraterrestrial civilization is too far away to contact us? Or what if we are simply considered too primitive to warrant contact? Could we then still somehow detect the existence of other civilizations? Possibly. An alternative to the classical, signal-based approach is to search for signatures of alien technology – like large-scale engineering projects, interstellar propulsion mechanism and industrial pollution in the atmospheres of exoplanets. Searches of this kind (sometimes called “new SETI”) make no assumption on the willingness of extraterrestrial civilizations to contact us directly, Moreover, non-detections resulting from suitable designed searches of this kind can yield meaningful upper limits on the prevalence of civilizations using the assumed technologies.
Project Hephaistos, named after the Greek god of blacksmiths who crafted much of the magnificent equipment of the Olympian gods (chariots, weapons and even automatons), belongs to this class of “new SETI” endeavours, focusing on the search for signatures of extraterrestrial technology rather than looking for signals deliberately sent our way.
Project Hephaistos, the first Swedish SETI project, has been made possible thanks to financial support from the Magnus Bergvall foundation and Nordenskjöldska Swedenborgsfonden.Logotype design: Genoveva Micheva
Erik Zackrisson (Project leader, Uppsala University)
Per Calissendorff (Stockholm University)
Saghar Asadi (Stockholm University)
Anders Nyholm (Stockholm University)
Beatriz Villarroel (Uppsala University)
Genoveva Micheva (Stockholm University)
George Xystouris (Uppsala University)
For more than 50 years, astronomers have searched the skies for artificial signals and other signs of extraterrestrial civilizations, yet no evidence of intelligent life beyond the Earth has so far emerged. We already know that planets are common - more than 2000 planets around other stars have already been detected (including several planets with properties reasonably similar to Earth). If one adopts the position that intelligent life should not be unique to our planet, this then leads to an apparent contradiction: If there is intelligent life beyond elsewhere in the Universe, why don’t we see any signs of this?
One viable explanation, among the many proposed for this so-called Fermi paradox, is that - even if planets and even primitive life is common – intelligent, technologically advanced lifeforms are extremely rare. Most SETI efforts have so far focused on our own cosmic backyard, the Milky Way galaxy, but if the probability for technologically advanced civilisations to arise is very small, we could well be alone in the Milky Way. If this is the case, our only chance of making a positive detection of extraterrestrial intelligence is to extend the search radius to extragalactic scales.
In the first project Hephaistos paper, we present a search for supercivilizations in a sample of more than 1000 galaxies similar to the Milky Way. Technically speaking, this search targets so-called Kardashev type III civilizations that have turned a fair fraction of the stars in their host galaxy into stellar engines (using a technology known as a Dyson sphere). While no strong Kardashev type III candidates are detected in our search, we are able to set an upper limit at 0.3% on the fraction of local disk galaxies hosting such civilizations. We also uncover a number of highly unusual galaxies that may open up new avenues for research within mainstream astronomy. We are now targeting these outliers for follow-up observations to learn more about the astrophysics underlying their extreme properties.
Extragalactic SETI: The Tully-Fisher relation as a probe of Dysonian astroengineering in disk galaxies [pdf]
Zackrisson, E., Calissendorff, P., Asadi, S., Nyholm, A. 2015, Astrophysical Journal, 810, 23
It may seems reasonable that sufficiently advanced and long-lived civilizations at some point will develop the means to communicate across interstellar distances, colonize other solar systems and perhaps even tap into the huge energy reservoirs locked up in stars or black holes. However, the way we imagine the motivations and technological feats of such civilizations is likely to be biased by our own position on the ladder of scientific and technological advancement. How does one sidestep such preconceptions, which are prevalent in essentially all current SETI endeavours?
An alternative to searching for specific forms of envisioned alien technology (power beams, Bracewell probes, Dyson spheres etc.) would be to conduct a more general search for phenomena that are not expected to occur naturally. Mining large astronomical catalogs for such anomalies could be a viable path to discover either new astrophysics or signs of extraterrestrial intelligence, and the scientific benefits would be great in either case. The challenge, of course, lies in distinguishing between the two interpretations. After all, many completely unexpected, yet perfectly natural astrophysical phenomena have been discovered throughout the history of astronomy. A case in point would be the discovery of pulsars, which for a brief period actually were considered to be potential alien beacons (see this paper by Alan Penny for an interesting account of this story), but for which a natural explanation was found, and ultimately generated a Nobel prize in physics. These difficulties aside, the method should of course be attempted.
In the second project Hephaistos paper, we present the first study of this type: A search for anomalies in scans of the night sky carried out a few decades apart. Since the lifetimes of stars range from millions to trillions of years, the night sky tends to be pretty stable over the course of a human lifetime. The most short-lived stars are also the rarest, and when the go, they tend to go with a bang. When we do witness the demise of massive stars, they are - with very few exceptions - at cosmological distances. No more than about one supernova per century is expected within a galaxy the size of the Milky way, and stars are not really expected to disappear without a trace from our own cosmic backyard over the course of a few decades. If relatively bright (and therefore nearby) objects were seen to disappear from the night sky, this would definitely be unexpected given our current understanding of astrophysics. Curiously, one tentative candidate for a disappearing object did in fact emerge from this pilot study (covering some ten million objects). This may well be a spurious source (i.e. the object was never there in the first place - it simply appears in the catalog because of a misinterpretation of noise) or a highly variable object (i.e. the object did not actually disappear, but simply fell below the detection threshold due to a drop in intrinsic luminosity), but we're certainly following up on this.
Our sky now and then − searches for lost stars and impossible effects as probes of advanced extra-terrestrial civilisations [pdf]
Villarroel, B., Imaz, I., Bergstedt, J. 2016, Astronomical Journal, in press
Simulated galactic colonization front after 10 million years, assuming von Neumann-type colonizers. The colour scale reflects the stellar density, with black indicating colonized regions. The left panel shows the simulated disk face-on and the right panel the same disk edge-on.Simulation by Saghar Asadi, Stockholm University
Simulated galactic colonization front after 180 million years, assuming von Neumann-type colonizers. The colour scale reflects the stellar density, with black indicating colonized regions. The left panel shows the simulated disk face-on and the right panel the same disk edge-on.Simulation by Saghar Asadi, Stockholm University
Galactic colonization based on von Neumann-type colonizers moving at 1% of light speed. Colonization efforts are assumed to cease once more than 75% of the stars have been colonized. At this point, the video speeds up to illustrate how the distribution of colonies evolves over time.Simulation by Saghar Asadi, Stockholm University
Galactic colonization based on von Neumann-type colonizers moving at 0.01% of light speed. Colonization efforts are assumed to cease once more than 75% of the stars have been colonized. At this point, the video speeds up to illustrate how the distribution of colonies evolves over time.Simulation by Saghar Asadi, Stockholm University
Erik Zackrisson (Associate Professor in Astronomy)
Phone: +46 (0)18 471 5975