New Technique for Finding Dyson Spheres in Gaia Data Release 2

SETI Astronomers have worked out a plausible way to find Dyson Spheres by using Parallax measurements from Gaia.

Published on 26th Apr, 2018

Consider supporting Space Fan News: to ensure you get current space & astronomy news each week! Hello Space Fans and welcome to another edition of Space Fan News. In this episode, on this day of the momentous second data release of the Gaia spacecraft, astronomers from the University of Uppsala in Sweden have been working on a way to find Dyson Spheres and other megastructures that may be around other stars in our galaxy that would provide our first confirmation of other civilizations in the Milky Way Galaxy. In a paper published on the preprint site Astro-ph this week, a group of SETI astronomers from the University of Uppsala in Sweden describe a technique for locating the signatures of star-covering artificial structures known as Dyson Spheres and any other suitably large megastructures that may be in orbit around a star. This comes in advance of the second data release of the Gaia mission which today released the most accurate positions ever made of 1.7 billion stars in our galaxy. For those who don’t know, a Dyson Sphere is a hypothetical sphere that covers all or part of a star. By constructing a Dyson sphere out of material from dismantled planets, extremely advanced civilizations could in principle tap into a significant fraction of the radiation power of their host star. Dyson spheres are typically not imagined as a solid shell, but rather as a dense, spherical swarm or shroud of absorbing satellites, with each satellite absorbing a small fraction of the stellar radiation. Other, less ambitious astro-engineering designs, where sparse swarms, rings or single large shades are built around both stars and stellar remnants have also been considered in the paper, and the time to build a small scale megastructure of this type has been estimated at as little as a hundred years. Who knows how long it would take to build a full-on Dyson Sphere. The paper outlines what a Dyson Sphere might look like in Gaia data. I’ve told you about Gaia a couple of times before on SFN but it is an ESA mission designed to accurately measure the positions of about a billion stars in our galaxy out to 30,000 light years with an accuracy never before achieved. Launched in December 2013, Gaia's mission is scheduled to last for five years. During that time, it will log the position, brightness and color of every visible celestial object that falls within its field of view. By repeating these observations throughout its mission, astronomers will be able to calculate the distance, speed and direction of motion of each of these objects, chart variations in their brightness, and determine whether they have nearby companions. From Gaia data, astronomers are able to get distances by measuring parallax, where you measure the shift in position of a star relative to the background stars, a standard trigonometric technique that astronomers have been using for hundreds of years but is only accurate for close stars between 500-1000 parsecs from Earth and Gaia is doing better than it’s ever been done. But there is another parallax method, called spectrophotometric parallax, which is a technique that works for stars much further out, out to about 10,000 parsecs from Earth, but it really only works with stars on the Main Sequence (which is fine, because we’re looking for civilizations here and Main Sequence stars are a good place to look). Spectrophotometric parallax measurements are done from ground-based observatories and there are many projects which compare the two methods as a sort of check on each other. OK so back to Dyson Spheres. Since a star surrounded by a partial Dyson sphere with a large fraction of the star being covered will appear unusually faint for its spectral type at optical and near infrared wavelengths, its spectrophotometric distance will be overestimated. Why? Because its faintness gives a false reading for it’s distance since it’s artificially covered. Spectra rely on flux or light output. A trigonometric parallax measurement, as provided by Gaia would, on the other hand, still be able to provide an accurate distance estimate - it is dependent only on its position relative to background stars. So, it should be possible single out tentative Dyson-sphere candidates by comparing parallax distances to their spectrophotometric counterparts. According to the paper, a large Dyson Sphere covering a large percentage of a star’s radiation power will appear to be closer to Earth in the Gaia data when computing the distance using the regular parallax method. However, because a star of a given spectral type would be much dimmer than expected (since it’s covered by a bunch of advanced civilization) the spectrophotometric parallax would be off, it would appear further away. So that means the trigonometric parallax provided by Gaia would reveal the true distance of the Dyson Sphere and comparing the two results computed from the Gaia dataset, any discrepancy should be a candidate star for more study. A shorter parallax distance of a star as compared to its spectroscopic parallax might indicate a Dyson Sphere or other megastructure in orbit around that star, and would definitely warrant a closer look. The authors of the paper also say that this technique will only work if the fraction of the star covered by the Dyson Sphere is significant, like more than 75% of the star’s radiation is blocked from us. Well that is it for this episode Space Fans, thanks to all of our Deep Astronomy Patreon Patrons who keep these episodes coming. Thanks to all of you for watching and as always, Keep Looking up! Paper "SETI WITH GAIA: THE OBSERVATIONAL SIGNATURES OF NEARLY COMPLETE DYSON SPHERES" Dyson Sphere Art by Adam Burn: Gaia DR2 Video: