GCSE Physics revision

The life cycle of a star

Solar system; stability of orbital motions; satellites (physics only)

AQA 4.8.1.2

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AQA student objectives

Learning pathway

ALL 🎯

Describe the life cycles of Sun-sized and much more massive stars, and explain how fusion forms new elements.

MOST 🎯🎯

Apply the scientific explanation of the life cycle of a star to a relevant example.

SOME 🎯🎯🎯

Analyse a new situation involving the life cycle of a star and explain the scientific reasoning.

Revision summary

Read on screen, then print for Cornell-style active revision.

A nebula is a large cloud of dust and gas that acts as the starting point for all stars.
Gravity pulls the dust and gas together, gradually forming a denser structure called a protostar.
As more particles join the protostar, its mass increases, strengthening its gravitational pull and attracting even more material.

1. The Nebula: Where It All BeginsAQA

A nebula is a large cloud of dust and gas that acts as the starting point for all stars.
Gravity pulls the dust and gas together, gradually forming a denser structure called a protostar.
As more particles join the protostar, its mass increases, strengthening its gravitational pull and attracting even more material.

Gravity compresses the protostar, increasing its density and causing particles to collide more frequently, which raises the temperature.
When temperature and pressure are high enough, hydrogen nuclei fuse together to form helium nuclei in a process called nuclear fusion.
Nuclear fusion releases enormous amounts of energy, heating the core and marking the transition to a main sequence star.

2. From Protostar to Main Sequence StarAQA

Gravity compresses the protostar, increasing its density and causing particles to collide more frequently, which raises the temperature.
When temperature and pressure are high enough, hydrogen nuclei fuse together to form helium nuclei in a process called nuclear fusion.
Nuclear fusion releases enormous amounts of energy, heating the core and marking the transition to a main sequence star.

During the main sequence stage, the outward pressure from nuclear fusion is perfectly balanced by the inward force of gravity.
This balance creates a long, stable period that can last for billions of years.
Our Sun is currently in the main sequence stage of its life cycle.

When a star runs out of hydrogen fuel, nuclear fusion stops and gravity causes the star to contract until it becomes hot and dense enough to restart fusion.
This new phase of fusion produces heavier elements, including all elements up to iron on the periodic table.
A small to medium-sized star, like our Sun, expands to become a red giant, whilst a much larger star expands to become a red supergiant.

4. Leaving the Main Sequence: Red Giants and Red SupergiantsAQA

When a star runs out of hydrogen fuel, nuclear fusion stops and gravity causes the star to contract until it becomes hot and dense enough to restart fusion.
This new phase of fusion produces heavier elements, including all elements up to iron on the periodic table.
A small to medium-sized star, like our Sun, expands to become a red giant, whilst a much larger star expands to become a red supergiant.

A red giant eventually becomes unstable and expels its outer layers of dust and gas into space.
The remaining hot, dense core is called a white dwarf, which emits light but no longer undergoes nuclear fusion.
Over time, the white dwarf cools and dims until it becomes a black dwarf, which no longer emits enough energy to produce visible light.

5. The Fate of a Red GiantAQA

A red giant eventually becomes unstable and expels its outer layers of dust and gas into space.
The remaining hot, dense core is called a white dwarf, which emits light but no longer undergoes nuclear fusion.
Over time, the white dwarf cools and dims until it becomes a black dwarf, which no longer emits enough energy to produce visible light.

Red supergiants undergo several cycles of expansion and contraction, producing increasingly heavy elements through nuclear fusion.
Eventually, a red supergiant explodes in a dramatic event called a supernova, which creates elements heavier than iron and ejects them across the universe.
The supernova is one of the most energetic events in the universe and marks the end of the red supergiant stage.

6. The Supernova: Death of a Red SupergiantAQA

Red supergiants undergo several cycles of expansion and contraction, producing increasingly heavy elements through nuclear fusion.
Eventually, a red supergiant explodes in a dramatic event called a supernova, which creates elements heavier than iron and ejects them across the universe.
The supernova is one of the most energetic events in the universe and marks the end of the red supergiant stage.

After a supernova, a very large star condenses into an incredibly dense core called a neutron star.
If the original star was truly massive, the remnant may collapse further to form a black hole.
A black hole has such strong gravity that it pulls in any nearby light, meaning no light is ever emitted and it appears as an empty, dark region of space.

7. Neutron Stars and Black HolesAQA

After a supernova, a very large star condenses into an incredibly dense core called a neutron star.
If the original star was truly massive, the remnant may collapse further to form a black hole.
A black hole has such strong gravity that it pulls in any nearby light, meaning no light is ever emitted and it appears as an empty, dark region of space.