8.1.4Space Physics
The Life Cycle of Larger Stars
5 min read 4 parts Lesson 4 of 10
Section 1 of 4Life Cycle of a Massive Star
A massive star lives a much shorter life than the Sun because it uses its fuel far more quickly.
1
A massive star forms from a collapsing cloud of gas and dust and spends a long time on the main sequence, fusing hydrogen into helium.
2
When hydrogen in the core runs out, the core contracts and heats while the outer layers expand, forming a red supergiant.
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Fusion then continues in the core and in shells around it, producing successively heavier elements, up to iron.
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The iron core can no longer release energy by fusion, so it collapses and the outer layers are blown away in a supernova explosion.
5
The remaining core becomes a neutron star or, if it is massive enough, a black hole.
Section 2 of 4Stages Compared with the Sun
The mass of a star determines how far fusion goes and what remains at the end of its life.
Main sequence
- Main sequence The stable stage in which hydrogen fuses into helium in the core, with gravity balanced by radiation pressure.
Red supergiant
- Red supergiant A very large, cool and luminous star formed after the core's hydrogen is used up.
Supernova
- Supernova A huge explosion that releases vast amounts of energy and scatters elements heavier than iron across space.
Remnants
- Remnants Neutron stars are very dense and made mainly of neutrons, while black holes are regions where gravity stops light escaping.
| Feature | Solar-mass star | Much more massive star |
|---|---|---|
| Giant stage | Red giant | Red supergiant |
| Ending | Planetary nebula and white dwarf | Supernova, then neutron star or black hole |
| Heaviest element made by fusion | Carbon and oxygen | Iron |
Section 3 of 4Why Mass Decides the Ending
Why Mass Decides the Ending
Element formation
- Element formation Stars fuse light elements into heavier ones, and supernovae produce the elements heavier than iron.
Energy balance
- Energy balance Fusion releases energy that balances gravitational collapse, so the star stays stable while its fuel lasts.
Mass decides fate
- Mass decides fate Larger stars burn their fuel faster and end their lives in supernovae, while smaller stars end more quietly.
Section 4 of 4Exam Checklist & Tips
8.1.4 – Key Points for the Exam
- Main sequence The long, stable stage in which a star fuses hydrogen into helium in its core.
- Red supergiant A very large, cool and luminous star at a late stage of a massive star's life.
- Supernova The explosion at the end of a massive star's life, which releases energy and scatters heavy elements.
- Neutron star A very dense remnant made almost entirely of neutrons, left after a supernova.
- Black hole An object so dense that its gravity prevents light from escaping.
Common Mistakes
- Stating that all stars become red giants and then white dwarfs;
- massive stars become supergiants and end in supernovae.
- Saying the Sun will become a supernova; it is not massive enough to do so.
- Claiming that supernovae happen because a star runs out of energy;
- the core collapses because fusion can no longer support its mass.
- Writing that fusion stops at helium in massive stars; heavier elements up to iron are formed.