About Project Hephaistos

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 60 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 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 ofnew 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)

Matías Suazo (Uppsala University)

Andreas Korn (Uppsala University)

Ansgar Wehrhahn (Uppsala University)

Project Hephaistos Paper I: SETI at Extragalactic Scales

For more than 60 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.

Paper link:

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

Project Hephaistos Paper II: Finding near-complete Dyson spheres with Gaia

The classical way to search for Dyson spheres is to look for their waste heat signatures at infrared wavelengths. While thermodynamical considerations suggests that this signature is more or less unavoidable, there are many naturally occuring infrared-bright objects in the Milky Way, so finding auxiliary signatures of Dysonian technology would be very useful. In the second project Hephaistos paper, we explore one such secondary indicator - discrepant distance estimates.

By studing the optical spectrum of a star, astronomers are able to deduce its intrinsic luminosity. By comparing its apparent brightness to this inferred absolute brightness, a so-called spectrophotometric distance can be derived - this is a standard way of estimating the distance to stars. However, a near-complete Dyson sphere will significantly dim the optical light of the star it surrounds, while likely not significantly interfere with the shape of its optical spectrum. This is likely to lead to a significantly overestimated spectrophotometric. The Gaia space mission, on the other hand, can measure distances through its parallax, which is not expected to be affected by the presence of a Dyson sphere. Hence, Dyson spheres candidates with a sufficiently high covering fraction should exhibit discrepancies between their parallax and spectrophotometric distances.

In this paper, we combine data from Gaia DR1 (which provides the parallax) and RAVE DR5 (which provides spectrophotometric distances using spectroscopy from a groundbased telescope) to look for objects with discrepant distance estimates. While there are 230 000 objects which feature in both these datasets, only about 8000 stars have sufficiently small errors to make the comparison meaningful. We single out a handful of stars for which the distances deviate in the way expected for a near-complete Dyson sphere, and discuss one of these, TYC-6111-1162-1, in more detail. While our follow-up observations bascially confirm the spectrophotometric distance from RAVE, temporal changes in its radial velocity suggest the presence of an unseen companion which could have gotten Gaia confused about its parallax (Update: later Gaia data releases essentially confirm this). Hence, TYC-6111-1162-1 is clearly not a good Dyson sphere candidate.

Paper link:

SETI with Gaia: The observational signatures of nearly complete Dyson spheres [pdf]
Zackrisson, E., Korn, A.J., Wehrhahn, A., Ritter, A. 2018, Astrophysical Journal, 862, 21

Project Hephaistos Paper III: Upper limits on partial Dyson spheres in the Milky Way

By combining data from large astronomical catalogs at optical and infrared wavelengths, it may be possible to identify partial Dyson spheres in the Milky Way, as these are expected as turn up in such data sets as objects with anomalously low optical brightness yet very high mid-infrared fluxes. In this paper, we set the stage for the largest Dyson sphere search to date, covering on the order of one hundred million objects with distances measured by the Gaia space mission.

Scanning the data for objects with characteristics similar to those expected for Dyson spheres constructed around main-sequence stars does however reveal plenty of interlopers, primarily in the form of young stellar objects, which sometimes display spectral energy distributions very similar to those expected for near-complete Dyson spheres. Even without weeding out such interlopers, it is nonetheless possible to set conservative upper limits on the fraction of Milky Way stars that may be hosting Dyson spheres. Here, we present such upper limits for Dyson spheres as a function of their covering fraction, temperature and distance. For example, less than 1 in 50000 stars within 100 parsec could potentially host Dyson spheres that are 90 percent complete and are operating at 300 K.

Paper link:

Project Hephaistos - I. Upper limits on partial Dyson spheres in the Milky Way [pdf]
Suazo, M., Zackrisson, E., Wright, J.T., Korn, A., Huston, M. 2022, Monthly Notices of the Royal Astronomical Society 512, 2988

Get In Touch

If you are interested in our work, then don't hesitate to get in touch. We're constantly looking for students interested in doing BSc/MSc projects in the field of SETI.

Contact details

Erik Zackrisson (Associate Professor in Astronomy)
Homepage: www.astro.uu.se/~ez
Email: erik.zackrisson[at]physics.uu.se
Phone: +46 (0)18 471 5975

If you are interested in SETI or astrobiology in general, Peter Linde has an excellent page with lots of information in Swedish: