I disagree with Imre. That "spiral" is not caused by reflections. The spiral seems to be occluding the star. Reflections can only add to the transmitted light.
That window has a screen installed, right? A screen completely explains the pattern since the wire in the screen does occlude the light coming from behind it. The screen was probably not visible in the viewfinder due to being out of focus, which is also why it's not obvious in the rest of the picture. However, nighttime starts are point light sources, so will reveal something like a screen that would otherwise be out of focus.
Taking pictures out windows is difficult at best, but you really don't want to do it thru a screen or if there is much light in the room. The room needs to be considerably daker than whatever you are photographing outside. At night that means the room needs be completely dark in practise. Take the picture outside already.