The Strangest (and Second-Strangest) Star in the Galaxy

Two ways to look at Tabby's Star: as intriguing data, or as an invitation to flights of fancy. (Credit: David Kipping, left; FantasyWallpapers.com, right) There’s an old saying: "Great discoveries don’t begin with ‘eureka!’; they begin with ‘that’s funny…’" I’ve long attributed the quote to the renowned science popularizer Isaac Asimov. Jason Wright gently corrects me. He has researched the line, he explains, and could find no evidence that Asimov ever spoke or wrote those words. It was a tidy encapsulation of what Wright is about. He is attracted to the peculiar side of science, and he is also a relentless sleuth. Wright, an astronomer at Penn State, is one of the lead researchers investigating the decidedly peculiar flickering object commonly known as Tabby's Star or, in the popular press, as the "alien megastructure star." The star's behavior is so puzzling that Wright included among the possible explanations that a huge construction project is orbiting around it. (Note that he never suggested aliens were the best explanation, merely that the hypothesis could not yet be ruled out.) Lately Tabby's Star has been acting up again, providing intriguing new data but, so far, still no definitive answers. While Tabby's Star continues to vex and excite the astronomical community, Wright is busy thinking about other puzzles as well. I was particularly intrigued by another misbehaving star, by the mouthy name of Przybylski’s Star (pronounced "jebilskee," roughly). If Tabby's Star is the most mysterious star in our galaxy--an epithet endorsed by Tabetha Boyajian, who first described the star's irregularities--then Przybylski’s Star may qualify as the second-most strange and mysterious star around. In this case, the puzzle is the star's composition, which appears to be filled with radioactive actinides, short-lived elements normally found only in nuclear experiments on Earth. I'm a sucker for unexplained scientific anomalies, so I caught up with Wright to hear his thoughts on these astronomical outliers. What follows is an edited version of our conversation. [For astronomy updates, follow me on Twitter: @coreyspowell] Tell me about Przybylski’s Star: What is it that makes this object so unusual? Its spectrum is extremely peculiar. Everyone who’s seen it says it’s the strangest stellar spectrum they’ve ever seen. It’s got an abundance pattern that is very hard to understand. In terms of exactly what abundances of what elements it’s showing us, I don’t know. Some people say there are so many lines you really can’t tell what you’re looking at. [Lines in a star's spectrum are used to identify its chemical composition.] But, they have to be the lines of some elements! And that’s what people try to figure out. Some of those elements appear to be short-lived radioactive isotopes, which makes no sense; such atomic nuclei should long ago have decayed and vanished. How can that be? The identification of short-lived isotopes seems like it must be wrong, because there’s no way to generate them. There is one clever way to hypothesize how they could be generated, however. [The hypothesis is that Przybylski’s Star contains as-yet undiscovered ultraheavy elements, which then decay into the short-lived byproducts we see.] It takes short-lived actinides being in there from being impossible to not totally impossible. The spectroscopic evidence points toward the short-lived nucleotides really being there. Our standard model for stars implies that the observation is probably wrong. But there's a small possibility that some really cool nuclear physics is going on in this star. There's another even further-out possibility, that intelligent aliens put the radioactive elements in there as a kind of chemical signpost... Carl Sagan and Iosef Shklovskii, along with Frank Drake, had raised the idea of looking for radioactive elements like promethium in stars as a possible alien signal. I found that sort of silly; why would aliens dump their promethium in stars? What would the point be? To get our attention, I guess, but I think there are easier ways to get our attention. It's neat that somebody said, Hey we should look for it, and then somebody else found something that seems to match what they predicted. But I wouldn’t put alien technology on a serious list of things that might be going on with Przybylski’s Star. [