Subject: Why are stars arranged in circles.

In many photos of star fields, there frequently are groups of
stars appearing as some portion of a circle. Often as if viewed
from some oblique angle. The "circle of stars"  is usually
an incomplete circle and often distorted. In some photos (most
of what I refer to is contained in the "Astronomy" magazine),
several can be seen.
Is this the result of supernovas occurring in the distant past?
Thanks for your answer!

Re: Why are stars arranged in circles.