The Life Cycle of Larger Stars (Edexcel IGCSE Physics)
Revision Note
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The life cycle of larger stars
After the main sequence, a high-mass star finishes its life cycle in the following evolutionary stages:
Red supergiant → supernova → neutron star (or black hole)
The key differences between a lower mass and higher mass star at this stage are:
A higher mass star will stay on the main sequence for a shorter time before it becomes a red supergiant
A lower mass star fuses helium into heavy elements, such as carbon, whereas a higher mass star fuses helium into even heavier elements, such as iron
Red supergiant
After several million years, the hydrogen causing the fusion reactions in the star will begin to run out
Once this happens, the fusion reactions in the core will start to die down
The star will begin to fuse helium which causes the outer part of the star to expand
As the star expands, its surface cools and it becomes a red supergiant
Supernova
Once the fusion reactions inside the red supergiant cannot continue, the core of the star will collapse suddenly and cause a gigantic explosion called a supernova
At the centre of this explosion, a dense body called a neutron star will form
The outer remnants of the star are ejected into space forming new clouds of dust and gas (nebula)
The heaviest elements are formed during a supernova, and these are ejected into space
These nebulae may form new planetary systems
Neutron star (or black hole)
In the case of the most massive stars, the neutron star that forms at the centre will continue to collapse under the force of gravity until it forms a black hole
A black hole is an extremely dense point in space that not even light can escape from
The life cycle of a high-mass star
The life cycle of a star much larger than our Sun
Examiner Tips and Tricks
Make sure you remember the life cycle for a high-mass star and that you can describe the sequence logically in case a 6-marker comes up in the exam!
Ensure you can clearly remember the end stages for a high-mass star (red supergiant, supernova, neutron star/black hole) as this is different for a star that is a similar size to the Sun!
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