Many theories have already been proposed to explain the mysterious dimming of Tabby's Star, also known as KIC 8462852. The star has been observed having unusual dips in brightness, which do not characterize other normal stellar objects that are slightly more massive than the sun.
It is suspected that the dimming of the star could be due to alien life. The idea is that a giant alien megastructure built by intelligent extraterrestrial life could be harvesting energy from the star, which causes its brightness to decrease.
Mysterious Signal May Be Due To Tabby's Star Eating A Planet
Another newer explanation for the star's unusual behavior is the theory that Tabby's Star swallowed an unstable planet.
"We propose that the secular dimming behavior is the result of the inspiral of a planetary body or bodies into KIC 8462852, which took place ~10 to 1e4 years ago," astronomers wrote in an April 2017 study. "Gravitational energy released as the body inspirals into the outer layers of the star caused a temporary and unobserved brightening."
Now another theory emerges. It suggests that the dimming over long periods is possibly caused by an uneven dust cloud that moves around the star.
Between January and December 2016, researchers observed the mysterious star in ultraviolet and visible light using data from NASA's Spitzer and Swift missions and the Belgian AstroLAB IRIS observatory.
They discovered less dimming in the infrared light from the star than in its ultraviolet light. Any object bigger than dust particles would equally dim all waves of light when it passes in front of the star.
New Theory Points At Circumstellar Dust
Huan Meng, from the University of Arizona, said that the alien megastructure theory cannot explain the wavelength-dependent dimming of the star. Meng and colleagues, who published in their study in The Astrophysical Journal on Oct. 3, think that a cloud of dust could be circling the star with an orbital period of about 700 days.
The researchers determined that the blocking particles are bigger than interstellar dust, the small grains located between the star and the Earth. These small particles cannot stay in orbit around the star since the pressure from the starlight would drive them farther away.
The best possible cause could be circumstellar dust that orbits a star. It is not so small it could fly away, but it is neither big enough to uniformly block the light in all wavelengths.
"The wavelength dependence of the fading favors a relatively neutral color (i.e., , but not flat across all the bands) compared with the extinction law for the general interstellar medium (), suggesting that the dimming arises from circumstellar material," the researchers wrote in their study.