CIE iGCSE Co-ordinated Sciences-P6.2.2 Life cycle of stars- Study Notes- New Syllabus
CIE iGCSE Co-ordinated Sciences-P6.2.2 Life cycle of stars – Study Notes
CIE iGCSE Co-ordinated Sciences-P6.2.2 Life cycle of stars – Study Notes -CIE iGCSE Co-ordinated Sciences – per latest Syllabus.
Key Concepts:
Core
1. Know that stable stars are formed as protostars from interstellar clouds of gas and dust due to gravitational attraction
2. Know that the next stages of the life cycle of a star depend on its mass, limited to:
(a) a small mass star (about the same mass as the Sun): red giant → white dwarf + planetary nebula
(b) a large mass star: red supergiant → supernova → neutron star
(c) a very large mass star: red supergiant → supernova → black hole
Supplement
3. Know that the nebula from a supernova may form new stars with orbiting planets
CIE iGCSE Co-Ordinated Sciences-Concise Summary Notes- All Topics
Formation of Stable Stars from Protostars
(a) Protostar Formation
- Interstellar space contains clouds of gas and dust, mainly hydrogen and helium.
- Gravitational attraction causes these particles to move closer and clump together.
- As the gas contracts, its density and pressure increase.
- The temperature rises due to the conversion of gravitational potential energy → thermal energy.
- This hot, dense, contracting body of gas is called a protostar.
(b) Formation of a Stable Star
- When the temperature at the core becomes high enough (≈ \( 10^7 \, \text{K} \)), nuclear fusion begins.
- Hydrogen nuclei fuse to form helium, releasing large amounts of energy.
- Fusion produces an outward radiation pressure and thermal pressure that balances the inward gravitational pull.
- This balance of forces makes the star stable — it has reached the Main Sequence stage.
- The Sun is currently a main sequence star, stable for billions of years.
Example
Explain why a protostar contracts before becoming a stable star, and what causes the contraction to stop.
▶️Answer/Explanation
Step (1): A protostar contracts because of gravitational attraction between particles in the cloud of gas and dust.
Step (2): As it contracts, temperature and pressure increase until nuclear fusion of hydrogen starts.
Step (3): Fusion releases energy, producing outward radiation and thermal pressure.
Step (4): This outward pressure balances the inward gravitational pull, stopping further contraction.
Final Answer: A protostar contracts due to gravity until nuclear fusion begins. Fusion generates outward pressure that balances gravity, forming a stable star.
Life Cycle of Stars Depending on Mass
(a) Small Mass Stars (≈ Sun’s Mass)
- After billions of years as a Main Sequence Star, hydrogen fuel runs out.
- The star expands and cools, becoming a Red Giant.
- Outer layers are ejected, forming a planetary nebula.
- The remaining hot dense core becomes a White Dwarf.
- Eventually, the white dwarf cools to a Black Dwarf (theoretical end stage).
(b) Large Mass Stars
- After main sequence, the star expands into a Red Supergiant.
- When nuclear fusion stops, the star collapses violently in a supernova explosion.
- The remnant core left behind forms a Neutron Star.
- Neutron stars are extremely dense, made almost entirely of neutrons.
(c) Very Large Mass Stars
- These stars also become Red Supergiants.
- They undergo a supernova explosion.
- The core’s gravity is so strong that it collapses further to form a Black Hole.
- A black hole has such strong gravitational pull that not even light can escape.
| Star Mass | Life Cycle Path | End Product |
|---|---|---|
| Small Mass Star (≈ Sun) | Main Sequence → Red Giant → Planetary Nebula → White Dwarf | White Dwarf → Black Dwarf (over very long time) |
| Large Mass Star | Main Sequence → Red Supergiant → Supernova → Neutron Star | Neutron Star |
| Very Large Mass Star | Main Sequence → Red Supergiant → Supernova → Black Hole | Black Hole |
Example
A star has a mass much greater than the Sun. Describe its life cycle after the main sequence stage and state its final outcome.
▶️Answer/Explanation
Step (1): The star expands into a Red Supergiant.
Step (2): When fusion stops, it collapses in a violent Supernova explosion.
Step (3): The remnant core is so dense that it collapses under its own gravity.
Final Answer: The star ends as a Black Hole if its mass is extremely large, otherwise as a Neutron Star.
Formation of New Stars from Supernova Nebula
- When a massive star reaches the end of its life, it explodes in a supernova.
- The explosion throws huge amounts of gas and dust (a nebula) into space.
- This nebula is rich in heavy elements (like carbon, oxygen, iron) formed during nuclear fusion inside the original star.
- Gravitational attraction causes regions of the nebula to contract and clump together.
- These dense regions can form new protostars, which eventually develop into stable stars.
- Surrounding dust and gas may come together to form orbiting planets, moons, asteroids, and comets — creating new planetary systems.
- This recycling process explains why Earth and other planets contain elements heavier than helium — they were made in earlier generations of stars.
Example
Explain how the material from a supernova contributes to the formation of new stars and planets.
▶️Answer/Explanation
Step (1): A supernova explosion releases large amounts of gas and dust into space, forming a nebula.
Step (2): Gravity causes parts of this nebula to collapse and form protostars, which later become new stable stars.
Step (3): The leftover material around the young star can form orbiting planets and other bodies.
Final Answer: The nebula from a supernova recycles matter, leading to the formation of new stars and planets, allowing elements like carbon and iron to exist in planetary systems such as our Solar System.