Extragalactic Seti: The Tully–fisher Relation as a Probe of Dysonian Astroengineering in Disk Galaxies

Abstract

If advanced extraterrestrial civilizations choose to construct vast numbers of Dyson spheres to harvest radiation energy, this could affect the characteristics of their host galaxies. Potential signatures of such astroengineering projects include reduced optical luminosity, boosted infrared luminosity and morphological anomalies. Here, we apply a technique pioneered by Annis (1999) to search for Kardashev type III civilizations in disk galaxies, based on the predicted offset of these galaxies from the optical Tully-Fisher relation. By analyzing a sample of 1359 disk galaxies, we are able to set a conservative upper limit of 3% on the fraction of local disks subject to Dysonian astroengineering on galaxy-wide scales. However, the available data suggests that a small subset of disk galaxies actually may be underluminous with respect to the Tully-Fisher relation in the way expected for Kardashev type III objects. Based on the optical morphologies and infrared-to-optical luminosity ratios of such galaxies in our sample, we conclude that none of them stand out as strong Kardashev type III candidates and that their inferred properties likely have mundane explanations. This allows us to set a tentative upper limit at 0.3% on the fraction of Karashev type III disk galaxies in the local Universe.

Galactic habitability re-examined: indications of bimodality

“…It is interesting to speculate that hypothetical advanced technological civilizations arising in dwarf galaxies would have an easier route to dominating their stellar systems than those arising in giants like the Milky Way. Hence, new and innovative research programs such as the G-hat survey for high Kardashev Type civilizations (Wright et al, 2014b,a;Griffith et al, 2015) or the search for dynamical-mass outliers (Annis, 1999;Zackrisson et al, 2015) should be extended to these kinds of objects; obviously, the latter method would need to be modified to use correlates of the dynamical mass other than the Tully-Fisher relation.…”

A probabilistic analysis of the Fermi paradox in terms of the Drake formula: the role of the L factor

“…h) This original presentation allows one to display quantitatively in a single figure (Fig. 5) and in a compact form, the three physical explanations mostly discussed as solutions to the Fermi paradox(see Webb 2015, and references therein): rare civilizations (low N ), too short-lived (low L, making them unable to arrive here, even if they are numerous and/or expand rapidly), or unable to expand at sufficiently high speed (low υ).…”

“…The case of υ/c=0.9 is shown only for illustration purposes, as it is improbable that civilisations may expand at such high speed (and even at υ/c=0.1), because the spaceships should travel even faster than that. In Prantzos (2013) it is argued that if N is "small" (arbitrarily taken to be N<100) the dozens of various "sociological" hypothesis put forward to explain Fermi's paradox (Webb 2015) may really constitute an answer for the absence of extraterrestrials on Earth. In that case, one may consider that Fermi's question does not constitute a true paradox.…”

“…These studies reached different conclusions on the paradoxicality of Fermi's question, both from the quantitative and the qualitative point of view, e.g. the timescales required for colonization of the Galaxy (Webb 2015;Ashworth 2014); however, none of those works makes explicit use of the Drake formula.…”

Fermi's Paradox Is a Daunting Problem—Under Whatever Label

“…Research that deals with FP has greatly expanded in recent years on both a theoretical and observational stage (Davies 2010(Davies , 2012Vukotid and Dirkovid 2012;Barlow 2013;Hair and Hedman 2013;Davies and Wagner 2013;Armstrong and Sandberg 2013;Lampton 2013;Cartin 2014;Nunn, Guy, and Bell 2014;Wright et al 2014;Spivey 2015;Griffith et al 2015;Zackrisson et al 2015 -to give just a few post-2010 examples). Not all of these papers have been authored by astronomers or astrobiologists; the multidisciplinary nature of the whole effort is seen in titles such as "The Fermi Paradox and Coronary Artery Disease" in one of the world's most prestigious medical journals (Gottlieb and Lima 2014), and the subject matter is discussed even by personalities such as the (in)famous NSA whistleblower Edward Snowden.…”