Sky and Telescope - June 2017 - 4

SPECTRUM

by Peter Tyson

A Mystery for the Age

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EVERYBODY LOVES A CLIFFHANGER, and Tabby's star delivers a

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N ASA / JPL- CA LTECH / R. HURT (IPAC)

doozy. As many S&T 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
Could a collision of comets or asteroids
discovery, astronomers have examined
(seen here in an artist's concept) have
Tabby's star with both space- and grounddimmed the light from Tabby's star?
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?

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Sky and Telescope - June 2017

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