Julius K. answered • 12/02/19
Well-rounded scientist who specializes in Chemistry & Physics
Stars typically fuse Hydrogen into Helium to generate massive amounts of heat and light. Depending on how massive the star is, when it runs out of Hydrogen it will either cease fusion or continue fusion by fusing Helium together.
This is because in less massive stars, the pressure put on the core (where fusion takes place) by gravity isn't enough to counter the outward force that fusion exerts. If however, gravity is strong enough to overcome that outward force due to fusion, fusion may still be able to take place. This cycle can essentially continue as long as the star is massive enough and the elements in the core have a low enough mass to allow fusion to happen.
The hard limit appears to be Iron. At that point, the Iron nuclei are so tightly bound that it would take more energy to fuse than it would produce, which would cool the star down.
tl;dr Iron is the heaviest element you'll find in a star with a really high mass.
