Dust cloud could be reason for strange dimming of Tabby’s star

 In Science
Tabby's star (KIC 8462852).

This illustration depicts a hypothetical uneven ring of dust orbiting KIC 8462852, also known as Boyajian’s Star or Tabby’s Star. Image & Caption Credit: NASA/JPL-Caltech

The unusual dimming of Tabby’s Star, for which a variety of explanations, including an alien “megastructure”, have been proposed, is likely caused by an irregularly shaped dust cloud orbiting the star, according to a new study.

Located in the constellation Cygnus, approximately 1,280 light-years from Earth, KIC 8462852, also known as “Tabby’s Star” or “Boyajian’s Star”, exhibited strange fluctuations in brightness seen by the Kepler Space Telescope during its primary mission searching the region for exoplanets.

Kepler Space Telescope

Artist’s rendition of the Kepler Space Telescope observing a star. Image Credit: NASA

Kepler observed several patterns of dimming by the star, including a 20 percent reduction in brightness over just several days.

The telescope also saw longer-term, subtler dimming patterns, one of which is still underway.

Because the brightness reductions of Tabby’s Star were nothing like those seen in normal stars, some citizen scientists studying it through Zooniverse‘s Planet Hunters program described the star as “interesting” and “bizarre”.

The unusual phenomenon prompted a variety of possible explanations, including a nearby swarm of comets, the star devouring a planet, and even a “megastructure” built by an advanced alien civilization to use the star’s energy as a power source.

In 2016, Tabetha Boyajian of Louisiana State University at Baton Rouge led a study of the star, which resulted in it being unofficially nicknamed in her honor.

After serving as lead author on a paper documenting that study, Boyejian took part in a follow-up study in which the star was observed with NASA’s Spitzer and Swift missions as well as with the ground-based Belgian AstroLAB IRIS observatory between January and December of 2016.

Spitzer observed Tabby’s Star in the infrared while Swift viewed it in ultraviolet light, and AstroLAB IRIS, a 27-inch (68-meter) reflecting telescope, studied it in visible light.

The year-long study revealed the star dimmed less in the infrared than in the ultraviolet, providing scientists with an important clue that implicated a cloud of dust as the cause.

Any object larger than a dust particle passing in front of a star would cause equal dimming in all wavelengths, as opposed to the unequal dimming seen in Tabby’s Star.

“This pretty much rules out the alien megastructure theory, as that could not explain the wavelength-dependent dimming,” noted Huan Meng of the University of Arizona and lead author of the most recent study, whose results have been published in The Astrophysical Journal. “We suspect, instead, there is a cloud of dust orbiting the star with a roughly 700-day orbital period.”

Illustration of star KIC 8462852 (Tabby's star) behind a shattered comet

This illustration shows a star behind a shattered comet. Observations of the star KIC 8462852 by NASA’s Kepler and Spitzer space telescopes suggest that its unusual light signals are likely from dusty comet fragments, which blocked the light of the star as they passed in front of it in 2011 and 2013. The comets are thought to be traveling around the star in a very long, eccentric orbit. Image & Caption Credit: NASA/JPL-Caltech

Researchers think the dust grains that make up the cloud are no larger than several micrometers, or one ten-thousandth of an inch, in diameter.

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