blurred edge with circles

[DilyanaB.]

Hello there, 

how can I create a circle with a blurred edge and transparent space inside? Here is an example. My problem is, that I already created a circle with a blurred edge, but I cannot make a space transparent inside. The transparent space inside is relevant for the image I will use. Do you have any ideas how can I do this? 

I appreciate your answer.

[edgrimley]

If I understand you correctly, make a circle with just a stroke and no fill. Blur the stroke.