Vortex star trails

This is my first attempt at making this "vortex" star trails I've seen from some other photographers.

 

UPDATE: This is a small tutorial I wrote on how I processed this photo: www.sgarciarill.com/vortex-star-trails-tutorial/

 

I believe the other photos (Particularly Lincoln Harrison who was my main inspiration) use a custom device to zoom in while making the exposure, but I did it in post processing with an old sequence of 130 photos I took at Garner State Park during the Eta Aquarids meteor shower in 2013.

Done