Can anyone explain how that ring of star forming region formed?
Hi @choucroute and welcome to Galaxy Zoo,
This is an Illustris image, so it is actually a simulated galaxy. You can find out more information regarding this project in this post.
Most of the star formation in galaxies occurs in the spiral arms, so it is not surprising for it too sometimes appear as if it is forming a ring 😃
Hope this helps and please let us know if you have any other questions!