Possibly The Coolest Thing I've Ever Read...

Scientists look at stars.  While doing so, they match the amount of light to the amount of heat being measured to determine a star's properties and classify it.

So why are some stars showing much less light than the amount expected, based on how much heat they're radiating?

One possible explanation is that these stars are sending less light out into the universe because it's being blocked artificially by a Dyson Sphere.  

What's a Dyson Sphere, you ask?  It's a hypothetical construction by a hypothetical alien race.  The concept is that this hypothetical race has advance to a point where they can surround their star with a massive construction that would harvest the energy of the star for use by their civilization.

I admit, when I envision a Dyson Sphere, I imagine a huge solid shell around a star with the inhabitants living inside it, but the more likely configuration would be what's termed a "Dyson Swarm" which would take the form of many satellites orbiting the star rather than a solid shell.  A civilization could harvest a fraction of the star's radiated energy using this method and that would more than satisfy their total energy needs.

If an alien race did all this, the signature would be a star whose visible light did not match its heat profile and scientists have found a bunch of stars with this exact signature.

The whole article is here and it's a FASCINATING read.