Dust cloud surrounding Tabby's Star may be causing strange dimming
Latest observation shows dimming is not equal in all wavelengths.

By Laurel Kornfeld | Jul 28, 2017

An irregularly-shaped dust cloud is the likely cause of the strange dimming of Tabby's Star, a phenomenon that has puzzled scientists since it was first observed in 2016.

Also known asKIC 8462852 or Boyajian's Star, the object experienced unusual dimming of up to 20 percent over just several days by the Kepler Space Telescope, which searches star systems for exoplanets.

Its dimming patterns are so unpredictable and atypical for normal stars that citizen scientists studying it as part of Zooniverse's Planet Hunters program described it as "bizarre" and "interesting."

Various explanations were proposed for the star's strange dimming, including a swarm of comets, swallowing of an orbiting planet, and even an alien "megastructure" constructed by an intelligent extra-terrestrial civilization to harness the star's energy.

Tabetha Boyajian of Louisiana State University at Baton Rouge, for whom the star is informally named, acted as lead author of a study on it in 2016 and is a co-author on a new study based on observations of the star with NASA's Spitzer and Swift missions and with Belgium's AstroLAB IRIS observatory.

Observations of the star in the infrared were conducted using Spitzer while those in the ultraviolet were done with Swift. AstroLAB Iris, a ground-based 27-inch (68-meter) reflecting telescope, viewed the star in visible light. All the observations were done between January and December 2016.

This latest study showed the star exhibiting less dimming in infrared light than in ultraviolet light.

If an object larger than a dust grain passed in front of the star, it would dim equally in all wavelengths. The fact that this does not happen strongly indicates the dimming is caused by an unevenly-shaped dust cloud in orbit around the star.

"This pretty much rules out the alien megastructure theory, as that could not explain the wavelength-dependent dimming. We suspect, instead, there is a cloud of dust orbiting the star with a roughly 700-day orbital period," explained Huan Meng of the University of Arizona at Tucson and lead author of a paper on the findings published in The Astrophysical Journal.

Individual dust grains in the cloud are estimated to be at most a few micrometers wide, or one ten-thousandth of an inch.

The significant level of dimming in the ultraviolet indicates the dust grains are larger than those found in interstellar space.

Individual grains of circumstellar dust, such as the type that surrounds Tabby's Star, are too small to block stellar light in all wavelengths.

A swarm of comets may still be orbiting the star and causing the shorter term, deeper dimmings. While an orbiting dust cloud is the most likely cause of Tabby's Star's long-term dimmings, it is not sufficient to explain the 20 percent dimming over just three days seen by Kepler.

"Tabby's Star could have something like a solar cycle. This is something that needs further investigation and will continue to interest scientists for many years to come," said AstroLAB volunteer and physics PhD Siegfried Vanaverbeke.

 

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