Section 1 of 4Elements Made in Stars
1
Main sequence stars fuse hydrogen into helium, and this fusion releases the energy that powers the star.
2
In a red supergiant, helium fuses to form carbon, and further fusion creates nitrogen and oxygen.
3
Fusion continues in the most massive stars until iron is formed in the core.
4
Fusing iron absorbs energy rather than releasing it, so heavier elements are not made in this way.
Section 2 of 4Heavy Elements and Supernovae
Supernova
- The explosion provides the very high temperatures needed to form elements heavier than iron.
Dispersal
- The explosion scatters these newly formed elements into space, where they can form new nebulae.
New stars
- Nebulae enriched in heavy elements can form new stars and planetary systems.
Early Universe
- The early Universe contained mainly hydrogen and helium, because no stars had yet produced heavier elements.
Section 3 of 4Where Elements Come From
Where Elements Come From
Hydrogen
- Hydrogen was formed in the early Universe and is the fuel for fusion in most stars.
Carbon and oxygen
- Made in red supergiant stars by the fusion of helium nuclei.
Up to iron
- Made by fusion in high-mass stars before their cores reach the iron stage.
Heavier than iron
- Made in the extreme conditions of supernova explosions and then ejected into space.
Section 4 of 4Exam Checklist & Tips
8.1.4 – Key Points for the Exam
- Element A substance made of atoms that all have the same number of protons.
- Stellar fusion Nuclear fusion occurring in the core of a star.
- Red supergiant A late stage of a high-mass star in which the outer layers have expanded and cooled.
- Heavy element An element heavier than iron, formed in supernovae.
- Nebula A cloud of gas and dust that may form new stars and planets.
Common Mistakes
- Saying that stars fuse elements heavier than iron in their cores; fusion in stars stops at iron.
- Claiming that the Sun currently makes carbon or iron; the Sun is fusing hydrogen into helium.
- Believing the early Universe contained many heavy elements; it was made mostly of hydrogen and helium.