"To explain the Fermi paradox needs a big killer, like an innocent looking physics experiment that sterilizes a solar system."
As I've mentioned elsewhere: Gamma Ray Bursts
As I've mentioned elsewhere: Gamma Ray Bursts
I had missed the full argument. [Embarrassing :-)] The one I had seen was that closer to the galaxy centre there would be a higher frequency of supernovas per cubic light year, while too far out there would be too little of the heavier elements from supernovas.