Within our own galaxy, some astronomers believe there may be a massive piece of alien technology, built to harvest energy from a distant star. The star, KIC 8462852, also known as Tabby’s Star, exhibits strange behavior, flickering and dimming, that can’t be explained by any known astronomical phenomena
Though there’s been no proof of this hypothesis, it also can’t be ruled out. The other theories, including that the star is blocked by the debris of a smashed planet, or that the dimming is caused by what’s known as “gravity darkening,” would go towards explaining parts of the phenomenon, but no current theory could explain it entirely.
I’m going with debris.