IB MYP 4-5 Physics- Life cycle of a star- Study Notes - New Syllabus
IB MYP 4-5 Physics-Life cycle of a star- Study Notes
Key Concepts
- Life cycle of a star
Life Cycle of a Star
Life Cycle of a Star
Nebula
- All stars begin as a cloud of gas and dust called a nebula.
- Gravity causes the nebula to collapse, forming dense regions called protostars.
- Temperature and pressure in the core increase as the cloud collapses.
Protostar
- The protostar forms as gravity pulls matter together.
- Nuclear fusion has not started yet, but temperature and pressure rise.
- If the protostar gains enough mass, fusion begins, and it becomes a main-sequence star.
Main-Sequence Star
- This is the longest phase in a star’s life.
- Hydrogen in the core fuses into helium, releasing energy and balancing gravity (hydrostatic equilibrium).
- Examples: Sun (medium-sized), Sirius (massive).
Red Giant / Supergiant
- Once hydrogen runs out in the core, fusion slows, and the core contracts while outer layers expand.
- Low- to medium-mass stars become Red Giants; massive stars become Supergiants.
- Helium fuses into heavier elements like carbon and oxygen.
Final Stages
- Low- to Medium-Mass Stars: Shed outer layers → form a planetary nebula. Core becomes a white dwarf → slowly cools into a black dwarf.
- Massive Stars: Undergo supernova explosion → leaves behind a neutron star or, if massive enough, a black hole.
- The heavy elements produced in supernovae enrich space and form new stars and planets.
Example:
Describe the life cycle of a star with a mass similar to the Sun.
▶️ Answer/Explanation
Step 1 – Formation: The star forms from a nebula and becomes a protostar.
Step 2 – Main Sequence: Hydrogen fuses into helium in the core; the star remains stable for billions of years.
Step 3 – Red Giant: Hydrogen is depleted; the core contracts, outer layers expand, helium fuses into carbon and oxygen.
Step 4 – Final Stage: Outer layers are ejected as a planetary nebula; the core becomes a white dwarf, cooling over time.
Example:
What happens to a star much more massive than the Sun at the end of its life?
▶️ Answer/Explanation
Step 1 – Main Sequence: The star fuses hydrogen into helium like any star.
Step 2 – Supergiant Phase: After hydrogen is exhausted, the star expands, fusing heavier elements in successive shells.
Step 3 – Supernova: The core collapses, causing a massive explosion (supernova), dispersing heavy elements into space.
Step 4 – Remnant: The core becomes a neutron star or a black hole, depending on the original mass of the star.