https://phys.org/news/2018-07-galaxy-outskirts-grounds-dying-massive.html

Using data from the Lick Observatory Supernova Search, a survey of nearby galaxies, the team compared the supernovae rate in outer spiral galaxies with that of known hosts—dwarf/satellite galaxies—and found comparable numbers for typical spiral outskirts and typical dwarf galaxies, roughly two core-collapse supernovae per millennium.

The study, "Supernova Rate beyond the Optical Radius," will appear in an upcoming issue of Astrophysical Journal Letters.