There's a simpler and more paranoid explanation available. This is an alien home planet, and it's actually emitting huge amounts of various types of light. Our astronomical instruments, however, have been hacked to not show any of that- we're not supposed to know about alien civilizations, as it would stunt our development. Somealien didn't think this through and simply removed all the light from our data on that planet, resulting in an anomalously dark appearance. It's a software bug. Perhaps it'll be fixed by the next time we look at that planet, and it'll appear as a boring planet of standard appearance.