If anyone out there still believes that we have spotted the sign of an advanced civilization, or "alien megastructure," around KIC 8462852, I’m afraid we’ll have to state once again that the curious changes in the star’s light are absolutely natural.
KIC 8462852's unusualness was reported in a paper last year by Yale astronomer Tabetha “Tabby” Boyajian after the strange dips in light were discovered by the citizen science group “Planet Hunters.” The media got interested in Tabby’s star after another paper showed how the variations are consistent with a swarm of alien megastructures.
Follow-up observations showed that these “aliens” were unusually cool and quiet: there was no peculiar infrared emission from the star (a megastructure will produce a lot of heat) and the SETI institute didn’t detect any artificial radio wave sources. Large swarms of comets were considered to be the most likely explanations for the unusual irregular dip in luminosity.
However, a study last January indicated that KIC 8462852 had been dimming by huge amounts over a century. By using data from DASCH (Digital Access to a Sky Century @ Harvard), which contains astronomical data from 1885 to 1993, the study indicated that Tabby’s star had dimmed by 20 percent over the last 100 years.
This was puzzling, as the comet theory couldn't account for such elongated dimming. KIC 8462852 is a regular F-type star, slightly hotter and bigger than the Sun, so this apparent dimming was mysterious. As natural mechanisms couldn't properly explain the effect, some thought that the best explanation was aliens slowly stealing stellar material, causing Tabby’s star to grow periodically dimmer.
The answer is actually simpler. A new study, accepted for publication in the Astrophysical Journal, has showed that the difference in brightness across the last 20th century is due to the different telescopes used and not by an intrinsic change in Tabby’s star.
The team used the same DASCH database but looked at 94 standard stars of well-known luminosity. They were searching for potential bias in the catalog by comparing how these stars' luminosities had changed over time.
“In this case, we looked at variations in the brightness of a number of comparable stars in the DASCH database and found that many of them experienced a similar drop in intensity in the 1960’s,” said Professor Keivan Stassun, senior author of the study, in a statement.
“That indicates the drops were caused by changes in the instrumentation, not by changes in the stars’ brightness.”
Although KIC 8462852 is not a secret alien base, it remains one of the most interesting objects discovered by the Kepler space observatory. Its variations are still without proven explanations, and they will continue to puzzle astronomers for a long time to come.