The Life Cycle of Solar Mass Stars (Edexcel IGCSE Physics: Double Science)
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The Life Cycle of Solar Mass Stars
1. Nebula
- All stars form from a giant cloud of hydrogen gas and dust called a nebula
2. Protostar
- The force of gravity within a nebula pulls the particles closer together until it forms a hot ball of gas, known as a protostar
- As the particles are pulled closer together the density of the protostar will increase
- This will result in more frequent collisions between the particles which causes the temperature to increase
3. Main Sequence Star
- Once the protostar becomes hot enough, nuclear fusion reactions occur within its core
- The hydrogen nuclei will fuse to form helium nuclei
- Every fusion reaction releases heat (and light) energy which keeps the core hot
- Thermal expansion from fusion reactions occur within its core due to fusion and the force of gravity keeps the star in equilibrium
- At this point, the star is born, and it becomes a main-sequence star
- During the main sequence, the star is in equilibrium and said to be stable
- The inward force due to gravity is equal to the outward pressure force which results from the expanding hot gases inside the star
4. Red Giant
- After several billion 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
- This causes the core to shrink and heat up
- The core will shrink because the inward force due to gravity will become greater than the outward force due to the pressure dies down
- A new series of reactions will then occur around the core, for example, helium nuclei will undergo fusion to form beryllium
- As the core shrinks, more reactions will cause the outer part of the star to expand
- It will become a red giant
- It is red because the outer surface starts to cool
5. White Dwarf
- The star will eventually become unstable and eject the outer layer of dust and gas
- The core which is left behind will collapse completely, due to the pull of gravity, and the star will become a white dwarf
- The white dwarf will be cooling down and as a result, the amount of energy it emits will decrease
The lifecycle of a solar mass star
Exam Tip
Make sure you remember the life cycle for a solar mass star and ensure you can describe the sequence in a logically structured manner in case a 6 marker comes up in the exam!Ensure you can remember the end stages for a solar mass star clearly (red giant, planetary nebula, white dwarf) as this is different for a star that is much larger than our Sun!
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