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Not long ago, I wrote in this space about astronomers searching for planets (“The variation tells the tale", mintne.ws/1ERZjNe) somewhere in the heavens. Looking back at that essay now, it struck me that I didn’t spell out exactly why they are conducting such a search. If it isn’t obvious, it’s because where there are planets, there’s hope of life. And what a thing it would be to find signs of life somewhere in the universe.

In that previous essay, I mentioned that a variation in a star’s brightness would suggest it has a planet. That’s because as the planet orbits the star, it moves between the star and us, temporarily occluding it and reducing its apparent brightness. So, the search for planets is in effect the search for stars whose brightness varies regularly. That essay was prompted by the discovery of one such star, which actually has two planets orbiting around it.

Only a few months later, astronomers have announced that they have found another star whose brightness varies. But this variation may actually suggest something even more exciting than a planet, and astronomers are scrambling to understand what.

This star, KIC 8462852, is faint enough that it’s visible only through a telescope. We’ve used the Kepler Space Telescope—the one that’s stationed in space—for several years to look at it and thousands of other stars, hoping to detect such variation. Since this effort generated a huge amount of data, it was handed off to a large number of amateur astronauts—“citizen scientists", they were called—to see if they could detect such variation. Four years ago, some of these citizen scientists began paying closer attention to KIC 8462852. Why? Because the variation in its brightness is extremely unusual (“bizarre" was one description).

Other stars known to have a planet orbiting them dim periodically by about 2%. That’s typical. But KIC 8462852’s brightness once sank by 15% over a period of seven days. Later, over several weeks, there were several dips in brightness, all greater than 5% and one near 22%. The paper that reported these findings—KIC 8462852: Where’s the flux? by T.S. Boyajian et al—refers to “the exotic complex of dips", which gives you an idea of how deeply they have intrigued astronomers.

Could be instrument error, of course. The scientists carefully checked and rejected that possibility. Has to be something else. The sheer magnitude of the dimming suggests something enormous is going around that star. (Think of a fly circling a distant streetlight, then an albatross doing so: which will obscure more of its light?)

Boyajian and colleagues examined various possibilities: the remnants of a collision between asteroids or planets, a vast cloud of dust, the star itself being variable, a collection of comets. While they think the comets are the likeliest of these “natural" explanations, they are not fully convinced. And when natural explanations are not satisfactory, you start thinking of others.

The word is that the scientists are working on another paper that examines whether the dips might be caused by—ready for this?—an unimaginably huge engineering project by some remarkably advanced civilization.

Fanciful? Bizarre? Maybe. But try to think of what might blot out 20% of the light of the sun, once you’ve ruled out planets and comets and so on. Nothing on Earth, nothing that we 21st-century humans could even think of building, would qualify. But what if there was a life form, a civilization, that has evolved far higher technological capabilities than us?

Nikolai Kardashev, an astronomer in the old USSR, suggested in 1964 that we measure such civilizations by how much energy they consume. The lowest on this Kardashev scale would be those civilizations that use only the energy available on their planets. Up from there, those that can harness all the energy their home stars emit, unlike the tiny fraction of our Sun’s energy that reaches us and the tiny fraction of that we actually use. There’s more to the scale, but leave that for now.

How might a civilization trap all the energy its star gives off? In 1960, the mathematician and thinker Freeman Dyson suggested “an artificial biosphere which completely surrounds" the star. Now, he didn’t really mean a solid sphere, which would cause its own serious gravitational problems even if it could ever be built. He had in mind a series of structures around the star, for which he used the word “shell". For better or worse, though, the idea is now commonly referred to as a Dyson sphere.

Stop for a moment to think of how gigantic a Dyson sphere would have to be. To give you an idea, if we were to build one around the Sun, at Earth’s distance from the Sun, its area would be nearly 600 million times the surface area of our planet. There’s no way on earth to craft something like that.

But Dyson suggested that if we found evidence of such a structure, that would indicate a civilization vastly more technologically advanced than ours.

Is that what Kepler has found, staring at KIC 8462852?

Once a computer scientist, Dilip D’Souza now lives in Mumbai and writes for his dinners. A Matter of Numbers explores the joy of mathematics, with occasional forays into other sciences.

Comments are welcome at dilip@livemint.com. To read Dilip D’Souza’s previous columns, go to www.livemint.com/dilipdsouza

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