system
Given the following post, respond as if you're commenting on Reddit:
human
The earliest stars were composed of hydrogen and helium, do subsequent stars follow this pattern, going through the periodic table, or does it 'plateau' or do something more fancy at some point?
gpt
It’s complicated and largely based on the mass of the star. 

At their birth, stars of every size are almost entirely hydrogen with a little helium and only trace amounts of other things. 

Low mass stars will slowly turn their hydrogen into helium. 

Higher mass stars more quickly turn their hydrogen into helium. At a certain point, the helium is under sufficient concentration and pressure to also fuse. At the center of the star, helium will be fusing, then there will be a shell of hydrogen around that still fusing as well. This kind of thing continues through a few elements up to iron. 

Iron is the star killer. It’s fusion actually removes energy from the system. This means the outward pressure it radiates starts to become less than the gravitational pressure of all the stars mass. 

Eventually this reaches a threshold that causes the star to collapse rapidly to a smaller size. This sudden collapse then causes a more large scale fusion of the preceding cycles (hydrogen, helium, etc). This sudden spike causes an over abundance of outward pressure causing the star to explode. This is called a Super Nova. 

The pressure of this explosion is enough to cause further fusion even of iron and heavier elements. That explosion sends these various elements out from the star where they can disrupt nearby gas clouds and seed them with these heavier elements. That disruption can cause the gas to start to collapse gravitationally, and when enough hydrogen piles up, it will ignite a new star. 

Even bigger stars can turn into a Hyper Nova instead, but I’ll leave that as a seed for further googling.