[NKosmatos]

Or it could be the sun eating dragon :-)

Joking aside, it could be a Kardashev Type II (or higher) civilization. https://en.wikipedia.org/wiki/Kardashev_scale

They could have used a dense Dyson sphere to “suck” the energy of the star, but if that was the case we would be able to detect its infrared radiation. https://en.wikipedia.org/wiki/Dyson_sphere

Anyway, I prefer the giant star eating dragon alternative ;-)