Two New Developments On The Dimming Of Tabby's Star

A dust ring with thicker patches explains some, but not all of the odd features we have observed of KIC 8462852, also known as the Alien Megastructure Star. NASA/JPL-Caltech

For two years KIC 8462852 has puzzled astronomers with its strange changes in brightness. Two sets of newly published research have expanded what we know and discredited some explanations, but we're still far from a conclusive answer.

Also known as Tabby’s Star, Boyajian’s Star, and the Alien Megastructure Star, KIC 8462852 has undergone changes in brightness many times larger than any other F-type star we've seen. Numerous explanations have been proposed, with the idea that aliens were building a partial Dyson Sphere around it capturing the imagination.

Dr Tabetha Boyajian of Louisiana State University who, after being alerted by citizen scientists, brought KIC 8462852 to world attention, is part of a team that has expanded the range of light wavelengths in which the star has been studied. The researchers report in The Astrophysical Journal that data from the Swift and Spitzer space telescopes, along with a larger device on Earth, reveal a slow fading between October 2015 and December 2016 across the entire measured spectrum. The dimming is weakest at longer infrared wavelengths and strongest in the ultraviolet.

"This pretty much rules out the alien megastructure theory, as that could not explain the wavelength-dependent dimming," said Dr Huan Meng, a graduate student at the University of Arizona, Tucson, in a statement

Dust, however, blocks short wavelength light more than longer wavelengths – the reason sunsets are red. The pattern of dimming is consistent with dust particles that are a few micrometers across (0.0001 inches), a common size in disks orbiting stars, but, unlike interstellar dust, large enough not to be pushed away by stellar winds.

But this only explains part of the mystery. A dusty ring with an orbital period of about 700 days, and thicker patches within it, explains the long-term dimming of KIC 8462852, but not the short dips observed earlier this year or the brief falls in brightness of up to 22 percent that originally brought the star to the world's attention.

That announcement was followed by the release of a yet to be peer-reviewed paper (preprint on ArXiv.org) by Dr Josh Simon, of the Carnegie Institution, revealing observations of KIC 8462852 going back to 2006. Some measurements of KIC 8462852 preceding intensive study by the Kepler Space Telescope have been dug up before, including some that date back a century, and have proven very controversial. Widely spaced observations are insufficient for tracking such apparently erratic variation, however.

Simon used additional data from the All Sky Automated Survey, revealing periods of brightening in 2007 and 2014. "Up until this work, we had thought that the star's changes in brightness were only occurring in one direction – dimming," Simon said. "The realization that the star sometimes gets brighter in addition to periods of dimming is incompatible with most hypotheses to explain its weird behavior."

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