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A mystery for the age.

EVERYBODY LOVES A CLIFFHANGER, and Tabby's star delivers a doozy. As many S&cT readers know by now, this otherwise nondescript main-sequence star in Cygnus displayed a series of unpredictable and unexplained dimmings of its starshine in the four years the Kepler spacecraft observed it (S&T: Feb. 2016, p. 14). In that short stretch, the star's usual complement of photons streaming towards our planet diminished significantly no fewer than 10 times. The dips lasted from days to weeks and showed no regularity in duration, periodicity, or the "shape" of the light curve.

Perhaps most surprisingly, during these brief periods the amount of starlight from KIC 8462852--as Tabby's star is officially known--declined by anywhere from half a percent to a humongous 20%. Imagine how big an object out in space would have to be to block one-fifth of the Sun's light from reaching Earth! Hollywood could have a field day with that one.

As Benjamin Montet and Tabetha Boyajian (Tabby herself) describe beginning on page 16, astronomers are flummoxed by what caused the erratic drops. They've ruled out some possible culprits, such as a glitch in the Kepler instruments that recorded the dips. But they've been unable to either confirm or deny many other hypotheses. The answer to this riddle remains deliciously elusive.

What I like most about this who- or whatdunit is the wide net it has thrown. First brought to astronomers' notice by a citizen scientist, the strange dips have captured the attention of myriad amateurs and professionals. Since the discovery, astronomers have examined Tabby's star with both space- and ground-based telescopes, in optical, infrared, and submillimeter wavelengths. They've pored over modern and historical data. They've thrown at the problem all they know about the aging of stars, the formation of planets and solar systems, and the light-blocking potential of everything from moonlet-size planetesimals to vast interstellar clouds. They've even gone so far as to invoke an alien megastructure as a not-entirely-inconceivable perpetrator (S&T: March 2016, p. 16).

In essence, the stumper cooked up by Tabby's star's anomalous behavior is what astronomy is all about. As with pondering the night sky itself, it has appeal for everyone. Who among us Earthlings would not be fascinated to hear the solution to this celestial brainteaser, when and if it comes?

Caption: Could a collision of comets or asteroids (seen here in an artist's concept) have dimmed the light from Tabby's star?

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Title Annotation:SPECTRUM
Author:Tyson, Peter
Publication:Sky & Telescope
Article Type:Editorial
Date:Jun 1, 2017
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