You're out exploring no doubt around or near to the core area - it has, shall we say, a very dense amount of stars in cube formations and you're simply looking at one at the edge / corner piece.
That's an interesting explanation. However, there was nothing like that on the map. And, moreover, it instantly went away from full to zero after some jump. I would expent some gradual disapperance and change in shape while I was passing this "cube" by.
I think the sky texture is rendered as icosphere, so one of the triangles got buggy.
But of course we all know the
true reason:
illuminati.