There are some milestone objects on different scales of the universe.
- The star is a notable feature on a solar system scale
- The supermassive black hole is a feature on a scale of a galaxy
- ??
The tricky part is that I am looking for something localizable. Great attractors, galactic filaments, and other easily findable objects are features alright, but they are, unsurprisingly, very big and hardly bounded.
Are there any rare objects that appear only on a Hubble volume scale (a proper volume of $\sim (c/H_0)^3$), but have definable boundaries?
EDIT: The lifetime of these objects should be at least millions of years.
EDIT': Red spirals fit the kind of objects I am looking for, but unfortunately, they are not rare enough. As @ProfRob pointed out they are only two orders of magnitude less frequent than usual galaxies.
I think that as long as an object is more frequent than a quasar it is too common.