New studies of the star KIC 8462852, better known as Tabby's star, have disproved the theory that it is surrounded by an artificial space structure. The suggestion that Tabby is surrounded by a Dyson sphere came after the report on the strange changes in the star's luminosity. Tabby is generally an ordinary F-class star (slightly hotter and heavier than our Sun). The star is located in the constellation Cygnus, 1,480 light years from us.
Observations of KIC 8462852 have shown that the light from it is periodically obscured by many strange (possibly artificial) objects. Luminosity changes occur with a period of 100 days, as if some objects pass in front of the star and block some of the light emitted by the star.
The public became interested in Tabby's star following the publication of a report in October 2015 by a group of astronomers from the University of Pennsylvania. The report suggested that KIC 8462852 is surrounded by a luminous ring made of many artificial objects.
The excitement caused by this message forced the scientists of the SETI Institute to carefully study the star in search of radio signals of artificial origin. However, the search result was negative. No signals other than natural ones were found.
A new study, already published by the University of Louisiana, published in January 2016, has added fuel to speculation about the construction of mega-objects in space by an alien civilization. According to the study, the star's luminosity dropped by 20% in just a century. According to enthusiasts, this is evidence of the intensive construction of artificial objects that should capture the radiation of the star. Unlike a solid sphere that completely intercepts the radiation of a star, the Dyson sphere consists of a huge number of separate objects that perform the same role. However, such an area is undoubtedly easier to build.
However, a new study, already data from a report from the University of Louisiana, showed that there is no convincing evidence for such a theory of changes in the luminosity of a star. The report was made on the basis of data from the unique resource DASCH. This resource is owned by Harvard and consists of digitized photographic plates that were taken by Harvard astronomers during the period 1885-1993. Since the photographs were taken by completely different people and telescopes, it is doubtful that they reflect the actual change in the luminosity of the star.
As a result, two teams of astronomers (one amateur) conducted their own study of similar stars from the DASCH catalog and found that a similar drop in luminosity is found in many other stars. Scientists say that when looking at sources as diverse as photographs over a century, it is difficult to set limits on accuracy for each one individually. In other words, improvements in equipment are a much simpler and more natural explanation for the change in the luminosity of stars in photographs.
Even if you do not involve aliens to explain the oddities of KIC 8462852, it is still a very mysterious star. The planet hunters noted an unusual change in the star's brightness in 2009. The drop in luminosity was 1% per week, which is equivalent to the passage of a planet the size of Jupiter in front of a star. However, the brightness changes due to such a large planet would be symmetrical. A different picture was observed, as if the object (s) obscuring the star had an irregular orbit, say, like comets.
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In 2013, the phenomenon repeated itself, but in a much brighter version. The periodical darkening lasted 100 days and the star's luminosity at the minimum dropped by as much as 20%. According to calculations, such an effect could be caused by the passage in front of the star's disk of an object 1000 times larger than the Earth in area.
Many theories have been proposed to explain the oddities in Tabby's shine. Passing in front of a brown dwarf star (possibly a companion to the star), obscuring the effects of intergalactic gas or a huge comet. The latter explanation is worth considering in more detail. In theory, a similar phenomenon could be caused by the destruction of a giant comet into thousands of smaller ones. True, by that time, this could in no way explain the decrease in the star's luminosity by 20% over a century.
In conclusion, the scientists point out that although there is no need to use the version about aliens to explain the strangeness of KIC 8462852, nevertheless, we do not have an exhaustive theory about the natural nature of the phenomenon.