system
Given the following post, respond as if you're commenting on Reddit:
human
Do heavier elements remain closer to the core of stars?

When new atoms are fused in a star, does it mostly occur in the very center of the core? If so, do they usually remain there and eventually push  some of the remaining lighter atoms out/up and prevent them from fusing? Does this result in stratified shells of separated elements? What happens when this star goes nova?
gpt
It depends on the star. 

The very smallest of starts the, red dwarves, have convection currents that run through the entire thing, all the way into the deepest bit of the core, and this then pulls the helium made from hydrogen up and out, achieving a good mix of it throughout the star. This is part of what lets red dwarves last so very long. They barely use any fuel (relatively) and they get to use their entire star's mass because they mix it up so well. It's not just what's in and around the core that they get to use. 

Other stars yes, the fusion initially happens in the very core and the byproducts build up and doesn't burn (yet), and and they don't have convection currents running through the whole thing to get that good mix going. Rings of different types of burning form around this core as it ages and goes through its final stages, absolutely.