An artist's impression of a young star with a protoplanetary disk forming around it. Could this be enough to explain the dimming? ESO/L. Calcada / @Astro_Wright

Here we go again. That misbehaving, mysterious star – the one people want to believe is surrounded by an alien megastructure – is dimming again, and the sci-curious on the Twittersphere and Reddit has gone veritably crazy. Those with telescopes have trained them on the star, code-named KIC 8462852, hoping to catch a record of its weird, fluctuating spectra.

Here’s a little recap for the uninitiated. Back in 2015, astronomers having a gander at this particular star noticed that it was going through enormous dips in its brightness. This means one of two things, essentially – either something in front of it is blocking the light heading towards Earth, or a bizarre process within the star itself is causing it to temporarily get dimmer, like a small breeze interfering with the light of a candle.

Known as Tabby’s star – after Dr Tabetha Boyajian, the first author of the original study describing this phenomenon – scientists and plenty of the public have come up with a wide range of hypotheses to explain it. The most famous, of course, is that it’s some sort of alien megastructure, like a Dyson sphere, surrounding the star that is blocking out the light.

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Other theories have come and gone. There was the idea that it’s down to comets swarming around the star, which eventually disintegrate. That would neatly explain a period of dimming followed by an enlightening, but old photographic plates reveal that it’s been doing this since the 1890s.

Calculations show that in order for this to still be down to comets would require 648,000 of them, all more than 200 kilometers (125 miles) across – something that although not impossible is still extremely improbable.

Artist's impression of a disintegrating proto-planet, another explanation for the dipping light levels. NASA/JPL-Caltech

There’s been the suggestion that it’s a variable star. These come in a range of flavors, including “pulsating variables” that grow and shrink quite dramatically, and “eclipsing binaries”, which dim when a companion star moves in front of it. Our own main sequence star, the Sun, is a variable star – its energy output dims by 0.1 percent over an 11-year cycle.

The problem here is that Tabby’s star is an F-Type, another main sequence star that is very stable, and one that should only show a very small change in brightness. KIC 8462852 has seen its brightness dip by up to 3 percent in just four years.

Other suggestions – that it’s been consuming a fragmenting planet, or that a massive cloud of dust keeps obscuring it – have also fallen by the wayside. As for aliens, the Search for Extraterrestrial Intelligence Institute (SETI) have trained their scopes at it, and have not found any signals indicative of mechanically-generated heat.

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So, right now, we have no idea what’s going on. Hopefully this time, astronomers will spot something more conclusive.