7 février 2016

Une "mégastructure" extra-terrestre?

Je n'ai pas parlé de cette nouvelle quand elle est sortie parce que ça me semblait un peu idiot, mais comme le mystère s'épaissit, je me laisse tenter.

Il y a quelques mois, des astronomes ont détecté la présence d'objets massifs qui orbitent autour d'une lointaine étoile, bloquant en partie sa luminosité. Les théories ont fusé à propos de l'origine de ces corps célestes, allant d'un nuage de comètes à des mégastructures extra-terrestres.

Évidemment, la première hypothèse semble être la plus probable. Sauf qu'elle vient d'être éliminée:

Schaefer decided this unusual star deserved a second look. He averaged the data in five-year bins to look for slow, long-term trends, and found that the star faded by about 20 per cent between 1890 and 1989. “The basic effect is small and not obvious,” he says.

To confirm the fade was real, Schaefer went to Harvard to look at the original photographic plates and inspected them by eye for changes, a skill few astronomers possess these days. “Since no one uses photographic plates any more, it’s basically a lost art,” says Wright. “Schaefer is an expert at this stuff.”

Schaefer saw the same century-long dimming in his manual readings, and calculated that it would require 648,000 comets, each 200 kilometres wide, to have passed by the star – completely implausible, he says. 

(...) What about those alien megastructures? Schaefer is unconvinced. “The alien-megastructure idea runs wrong with my new observations,” he says, as he thinks even advanced aliens wouldn’t be able to build something capable of covering a fifth of a star in just a century. What’s more, such an object should radiate light absorbed from the star as heat, but the infrared signal from Tabby’s star appears normal, he says.

“I don’t know how the dimming affects the megastructure hypothesis, except that it would seem to exclude a lot of natural explanations, including comets,” says Wright. “It could be that there were just more dimming events in the past, or that astronomers were less lucky in the past and caught more dimming events in the 1980s than in the 1900s. But that seems unlikely.”

There’s no doubt KIC 8462852 is behaving strangely, so something must be responsible, says Schaefer. “Either one of our refutations has some hidden loophole, or some theorist needs to come up with some other proposal.”

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