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

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.

However, these dust grains are still bigger than those in interstellar space, which are too tiny to stay in orbit around the star.

Dust particles in orbit around a star, known as circumstellar dust, are large enough to remain in orbit but still too small to equally block starlight in all wavelengths.

Many who regularly follow Tabby’s Star are volunteers, including citizen scientists who serve as software and technical support for AstroLAB.

While some, such as physics Ph.D. Siegfried Vanaverbeke, are formally trained in astronomy, others, such as Franky Dubois, who operated AstroLAB during the study; Ludwig Logie, who provides technical assistance for the telescope, and Steve Rao, who processes images of Tabby’s Star’s brightness, do not have such formal training.

They were recruited for the follow-up study by George Rieke of the University of Arizona, who read the findings of the initial study and subsequently co-authored the latest journal article.

Questions remain regarding the variations in Tabby’s Star’s brightness, as a dust cloud explains the long-term dimming but not the rapid short-term dimming observed by Kepler.

The latter could be caused by a swarm of comets, according to researchers who studied the star with Spitzer and with NASA’s Wide-field Infrared Survey Explorer (WISE).

Comets are thought to be one of the most common sources of dust that orbit stars; therefore, they could also be related to the long-period dimming studied by Meng et al.

“Tabby’s Star could have something like a solar activity cycle,” Vanaverbeke proposed. “This is something that needs further investigation and will continue to interest scientists for many years to come.”

Future investigations will not be conducted by Kepler, which is now in its extended K2 mission studying other regions of the sky.

The most mysterious star in the universe by Tabetha Boyajian.
Video courtesy of TED Talk

 

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Laurel Kornfeld is an amateur astronomer and freelance writer from Highland Park, NJ, who enjoys writing about astronomy and planetary science. She studied journalism at Douglass College, Rutgers University, and earned a Graduate Certificate of Science from Swinburne University’s Astronomy Online program. Her writings have been published online in The Atlantic, Astronomy magazine’s guest blog section, the UK Space Conference, the 2009 IAU General Assembly newspaper, The Space Reporter, and newsletters of various astronomy clubs. She is a member of the Cranford, NJ-based Amateur Astronomers, Inc. Especially interested in the outer solar system, Laurel gave a brief presentation at the 2008 Great Planet Debate held at the Johns Hopkins University Applied Physics Lab in Laurel, MD.

Reader Comments

Back during the late 80s and early 90s, there was a great deal of discussion on the Extropy mailing list about dust-sized, orbiting computers, “computronium,” being made by advanced technical civilizations. I.e., just because it looks like dust, you can’t be certain it is natural.

Inspite of what one and one researcher claims, dust doesn’t rule out much. For example, I don’t believe it’s aliens but if aliens are building a megastructure they would stir up a lot of dust. The light curves are more suggestive of gigantic rings larger than the star itself than comets. In addition to the short term dimming events, there are long term periods that last for many years where the dimming slowly increases followed by a return to normal periods. My point is that the mystery is far from being solved.

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