Washington, Oct 5 (IANS): The unusual dips in brightness that a stellar object known as Tabby's Star experiences could be due to an uneven dust cloud moving around the star, not because of a "megastructure" built by an advanced civilization, says a new study.

The long-term dimming of the Tabby's Star, -- also known as Boyajian's star, or, more formally, KIC 8462852 -- has been found to be quite bizarre. NASA's Kepler space telescope even observed dimming of up to 20 per cent over a matter of days.

Scientists do not expect such behaviour for normal stars slightly more massive than the Sun.

Speculations have included the idea that the star, more than 1,200 light-years away from Earth in the constellation Cygnus the Swan, swallowed a planet that it is unstable, and a more imaginative theory involves a giant contraption or "megastructure" built by an advanced civilization, which could be harvesting energy from the star and causing its brightness to decrease.

The findings of the new study published in the Astrophysical Journal rule out the "alien megastructure" idea and the other more exotic speculations.

Using NASA's Spitzer and Swift missions, as well as the Belgian AstroLAB IRIS observatory, the researchers found less dimming in the infrared light from the star than in its ultraviolet light.

But any object larger than dust particles would dim all wavelengths of light equally when passing in front of Tabby's Star, the study said.

"This pretty much rules out the alien megastructure theory, as that could not explain the wavelength-dependent dimming," said lead author of the study Huan Meng from University of Arizona in the US.

"We suspect, instead, there is a cloud of dust orbiting the star with a roughly 700-day orbital period," Meng said.