The original star was noticed in 2015 when scientists noticed unusual fluctuations in the light from a star named KIC 8462852. This otherwise-normal F-type star, which is slightly larger and hotter than Earth's sun, sits about 1,480 light-years from Earth, in the constellation Cygnus.
However, when the researchers analysed data from NASA's Kepler space telescope, astronomer Tabetha "Tabby" Boyajian, then at Yale University, and her colleagues found dozens of odd instances of KIC 8462852 dimming by up to 22%, with such dips lasting anywhere from a few days to a week. These events did not appear to follow any pattern and seemed far too substantial to be caused by planets or dust crossing the star's face.
The analyses of KIC 8462852 — now nicknamed "Boyajian's star" – made researchers consider the possibility that they might have detected signs of intelligent alien life. Specifically, researchers have suggested that the star is surrounded by a Dyson sphere, a hypothetical megastructure that is built around a star to capture as much of its light as possible. Mathematician and physicist Freeman Dyson even made a bold suggestion that such megastructures could help power an advanced civilization. Further analyses have pointed to more prosaic explanations, such as clouds of dust or comet fragments.
Now, study author Edward Schmidt, an astrophysicist at the University of Nebraska-Lincoln, suggests that he may have discovered more than a dozen stars like Boyajian's star, with the same patterns. Schmidt looked for counterparts of Boyajian's star using software that searched for analogous dimming events from about 14 million objects with varying brightness monitored in the Northern Sky Variable Survey from April 1999 to March 2000, detailing his findings July 18 in The Astrophysical Journal Letters.
Using data from the All-Sky Automated Survey for Supernova, he followed up on promising candidates by examining their long-term behaviour, ruling out sources whose dimming could be caused by conventional explanations such as an eclipsing companion star or some intrinsic variability in brightness, and found at least 21 stars falling into the same category. Fifteen of them were nicknamed "slow dippers" that dimmed at rates similar to Boyajian's star, and six were "rapid dippers" that showed even more extreme variability in their dimming rates.
"The thing that surprised me the most were these stars that had so many dips, the ones I called 'rapid dippers,'" Schmidt told Space.com. "I expected more occasional dips like Boyajian's star."
Further analysis revealed that these potential dippers tended to be either conventional "main-sequence" stars with about the same mass as the sun or red giant stars with about twice the sun's mass. The slow and rapid dippers are seen in both groups, which may suggest that they represent varying degrees of the same mechanism, Schmidt said.
However, Schmidt noted that the Northern Sky Variable Survey did not contain records of Boyajian's star itself darkening during the year of data in that catalogue, meaning that there might be other stars that were missed.
"We're obviously missing some of these stars because of the catalogs we have," Schmidt said. "By looking at more catalogs, we may get a better picture of what's going on, even though it won't be a complete picture."
Schmidt is now intending to follow up on the “rapid dippers,” he said, noting that “at least one seemed to be slowing way down in its dipping rate over the five years of coverage we have of it. It'd be interesting to find out what happened in its past, which may help give a better idea of what's going on with these stars.”
