Unstable particles

Usage examples of kaons.

But if the electrons were converted to kaons, they could all occupy the lowest energy level, putting up much less resistance, and making the collapse of a smaller star into a black hole theoretically possible.

It in fact should rebound at some point, with the kaons spontaneously reconverting to electrons.

At that point, neutrinos should again be able to escape—at least until the process reverses, and the electrons turn back into kaons again.