“A splash in the cosmic pond”—Sagan describing ring galaxies. In a bulls-eye galaxy collision, there is an expanding shock front of star formation. Newly-formed but short-lived stars outshine the older ones by an order of tens of thousands, which is why only the expanding ring is readily visible.
What’s truly remarkable is that we are viewing this one from the “top”, from near one of the galactic poles, so it appears circular rather than elliptical. (Unless it is actually elliptical and we just have a luck viewing angle.) Note the guy in the background, at one O’clock who appears elliptical.