is boyajian's star evidence of extraterrestrial civilizations? -- 4/25/17

Today's selection -- from "Strange News from Another Star" by Kimberly Cartier and Jason T. Wright. The highly advanced Kepler space observatory was launched in 2009 and has surveyed for than 150,000 stars. Of those, only one -- Boyajian's star -- shows unexplained light fluctuations:

"One quiet afternoon in the fall of 2014 ... Tabetha Boyajian visited our astronomy department at Pennsylvania State University to share an unusual discovery. ... Then a postdoctoral scholar at Yale University, Boyajian had flagged inexplicable fluctuations of light from a star monitored by NASA's planet-hunting Kepler space telescope. The fluctuations looked nothing like those caused by a planet passing between the star and the telescope. She had already ruled out other culprits, including glitches in Kepler's hardware, and she was looking for new ideas. One of us (Wright) suggested something very unorthodox: perhaps the fluctuations in brightness were caused by alien technology.

Artist's impression of a Dyson swarm

"In the 1960s physicist Freeman Dyson postulated that advanced, energy-hungry civilizations might enshroud their home stars in solar collectors -- later called Dyson spheres -- to absorb practically all of a star's light. Could this fading star be the first evidence that other cosmic cultures were more than science fiction? That outré idea was a hypothesis of last resort, but for the time being, we could not dismiss it.

"The star that stumped Boyajian -- now officially known as Boyajian's star and colloquially called Tabby's star -- has captivated astronomers and the general public alike. Like all great enigmas, it has generated a seemingly infinite number of possible solutions -- none of which wholly explain the curious observations. Whatever is responsible may lie outside the realm of known astronomical phenomena.

"Before Kepler launched in 2009, most planet hunters doggedly revealed new exoplanets (planets orbiting other stars) one by one, like anglers pulling individual fish from the sea. Kepler came along like a trawler, scooping up new worlds thousands at a time.

"For four years the telescope continuously observed stars in one small patch of the Milky Way. It was looking for planetary 'transits,' in which fortuitously aligned worlds cross the face of their host stars and block a fraction of the starlight seen from Earth. Graphed over time, the brightness of a star is described by a so-called light curve. With no transiting planets, the curve will resemble a flat line. Add in a transiting planet, and that light curve will now include U-shaped dips that recur like clockwork each time the orbiting body blocks the star's light. The duration, timing and depth of the dips convey information about the planet itself, such as its size and temperature.

"Of the more than 150,000 stars Kepler surveyed, just one -- dubbed KIC 8462852, after its number in the Kepler Input Catalog -- displayed a light curve that defied explanation. Members of the Planet Hunters citizen science project were the first to notice it when they scoured Kepler's data for transiting worlds overlooked by professional astronomers' automated planet-hunting algorithms. KIC 8462852 showed transitlike dips in starlight seemingly at random, with some lasting a few hours and others persisting for days or weeks. Sometimes the star's light dimmed by about 1 percent (characteristic of the largest transiting exoplanets), but other times it plummeted by up to 20 percent. No conceivable planetary system could produce such an extreme and variable light curve.

"Perplexed, these citizen scientists notified Boyajian, a member of the team overseeing the Planet Hunters project. In 2016 they introduced the star and its mysteries to the world in a peer-reviewed journal article with the subtitle 'Where's the Flux?' (Boyajian calls KIC 8462852 the 'WTF star').

In this artist's illustration, a star's light is blocked by orbiting comets.

"Boyajian's star held yet more surprises. In the aftermath of her WTF paper, astronomer Bradley Schaefer of Louisiana State University claimed, based on archival data, that Boyajian's star had dimmed by more than 15 percent over the past century.

"The claim was controversial because such multidecadal dimming seems next to impossible. Stars stay at nearly the same brightness for billions of years after they are born and only undergo rapid changes just before they die. These 'rapid' changes take place on the timescale of millions (rather than billions) of years and are accompanied by clear markers that Boyajian's star lacks. According to every other measurement made, it is an unremarkable middle-aged star. There is no evidence that it is a variable star, pulsing with a regular beat. And there is no indication that it is accreting material from a companion star, no suggestion of anomalous magnetic activity, and no reason to think it might be young and still forming -- all phenomena that could rapidly alter its brightness. In fact, aside from its anomalous dimming, this star appears entirely ordinary.

"Yet Schaefer's claim held up when astronomers Benjamin T. Montet and Joshua D. Simon checked it with the original, lesser known Kepler calibration data. They found that Boyajian's star faded by 3 percent over the four-year Kepler mission, an effect as extraordinary as the shorter-term dips.

"We must now explain two mind-boggling phenomena related to Boyajian's star: slow dimming over at least four years (and possibly the past century) and deep, irregular dips spanning days or weeks. Although astronomers would prefer a single explanation for both, each phenomenon is difficult to explain on its own and even harder to explain when considered in tandem with the other."


Kimberly Cartier and Jason T. Wright


Strange News from Another Star


Scientific American


Copyright 2017 Scientific American


May 2017
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