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Tabby's Star's twinkle probably the boring business of calibration

Sorry, people, there is NO Dyson sphere out there

By Richard Chirgwin, 10 May 2016

Put the boffins in a cage and break out the popcorn: a new analysis suggests the “long-term decline” in the light observed from the hotly-speculated-upon “Tabby's star” tells us more about calibrating Earth instruments than alien gigastructures.

The fun began last year when Kepler images showed unusual flickers in the brightness of the star, formally known as KIK 8462852.

NASA played killjoy to the speculation that its odd twinkling was because an alien civilisation was building a Dyson sphere around the star, and that structure was absorbing its light. NASA far prefers the idea that it's a comet swarm absorbing light, but Louisiana State University astronomer Bradley Schaefer reckoned a hundred years of observations showed a long-term 20 per cent decline in the light reaching us.

Enter Vanderbilt's Michael Lund, who in the best traditions of a gloves-off boffin-bash has put a counter-paper to the Astrophysical Journal (motto: “The first rule of Fight Club is peer review”). Collaborators on the paper include Vanderbilt physics and astronomy prof Keivan Stassun, Lehigh University astronomer Joshua Pepper, and German amateur astronomer Michael Hippke who with NASA postdoctoral fellow Daniel Angerhausen had launched an independent analysis of the same data.

The problem with using a hundred years' of observations, the group argue, is that the source data from “Digital Access to a Sky Century @ Harvard includes half a million glass plates shot between 1885 and 1993, using a number of different instruments and cameras.

That's a formidable calibration challenge, the group argue in their paper (pre-press at Arxiv here), that makes it inevitable that when digitised, there will be variation in the magnitudes recorded for any particular star.

That doesn't matter for big variations – “in the order of magnitudes” (in this case referring to the magnitude, or brightness, of a celestial object) – but the 20 per cent decline in Tabby's star is down near the noise floor, the paper argues.

While that's another nail in the coffin of the “alien structure” theory, boffins will have plenty of fun poring over the Kepler data to work out what's causing the star to flicker. ®

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