Let extraterrestrials construct a Dysons sphere

But not a building by aliens

The star KIC 8462852 is the subject of wild speculation. Some researchers consider that it could be surrounded by a gigantic Dyson sphere. So they are on thin ice.

For several months, the star with the designation KIC 8462852 has been under close observation by astronomers. Mysterious fluctuations in brightness have raised the suspicion that the star could be surrounded by a gigantic structure with which a highly advanced civilization can harvest solar energy. That sounds far-fetched. Nevertheless, researchers at the Seti Institute did not let themselves be deterred from pointing a radio telescope at the star in November to search for signals from extraterrestrials - to no avail. Now the euphoria that KIC 8462852 has sparked in some circles has received another damper. A team of American and German astronomers has found no confirmation that the star has had behavioral problems for a hundred years.

Discovery by laypeople

A group of volunteers got the ball rolling. As part of a “Citizen Science” project, the planet hunters analyzed thousands of images that the Kepler space telescope had taken between 2009 and 2013. They noticed that the brightness of KIC 8462852 repeatedly decreases briefly, sometimes by 20 percent. A planet passing in front of the star could not be the cause. The distances between the short dark phases were too irregular and the kinks in the light curve were not symmetrical enough. But what else could be the reason?

Last year professional astronomers took on the matter. After an in-depth study of various scenarios, Tabetha Boyajian's group from Yale University came to the conclusion that the star's bizarre light curve can best be explained by a swarm of comet fragments or an asteroid belt. According to the researchers' calculations, the fragments must have come from a body that must have been at least a hundred kilometers long before it broke up.

At that time there was no remotely thought of artificial objects, says Kevin Heng from the University of Bern, one of the co-authors of Boyajian. He was all the more surprised when the discussion about extraterrestrials suddenly started.

A construct from aliens?

This possibility was brought into play by researchers at Pennsylvania State University. In a publication they pointed out that a swarm of artificial objects - such as huge solar collectors - could also cause such fluctuations in brightness. The name Dyson sphere has become common in the relevant literature for such constructs. It goes back to the physicist Freeman Dyson. In the 1960s, he had thought about how a highly advanced civilization could be recognized that is technically capable of fully utilizing the sunlight of its central star.

These considerations received a boost in January. Bradley Schaefer from Louisiana State University in Baton Rouge used archived images of the star to reconstruct that it is not only sporadically darkened. Superimposed on this is a continuous decrease in brightness between 1890 and 1989. According to Schaefer, this trend speaks against the comet hypothesis. According to his calculations, 648,000 comets, each 200 kilometers in size, would be needed to explain the continuous darkening. For comparison: the largest known comet in our solar system is Hale Bopp with a diameter of 60 kilometers.

If, on the other hand, the sporadic darkening is caused by artificial structures, the long-term trend would also be plausible. The continuous darkening of the star could then be an indication that the Dyson sphere surrounding the star has assumed ever greater dimensions over the past 100 years.

Not a significant trend

However, a stop is now being put to this wild speculation. Keivan Stassun's group from Vanderbilt University in Nashville took another closer look at the archived recordings on which Schaefer relies. These recordings were made with various telescopes and cameras. Before you can compare them, you have to estimate how big the systematic errors are. The researchers did that and found that the trend observed by Schaefer is not statistically significant. Other stars on the archived images also showed a similar trend. This indicates that the continuous decrease in brightness is not due to the stars, but to the instruments, Stassun is quoted in a press release from his university.

What the researchers do not question are the star's brief and erratic fluctuations in brightness. The cause has not yet been fully clarified. Therefore one does not have to use extraterrestrials. Heng is not surprised that the less spectacular answer turned out to be probably the right one. Extraordinary claims require extraordinary evidence, he says. However, the evidence for the Dyson Sphere was anything but extraordinary.