The Life of a Star
Stars are born, live for billions of years, then die — some quietly, some in a spectacular explosion. Follow the life cycle from a cloud of dust to a white dwarf, neutron star or black hole.
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The Life of a Star 🌟
Stars are not eternal — they are **born**, **live** for billions of years, and eventually **die**. The Sun is a middle-aged star right now. How a star ends depends on one thing above all: its **mass**. Follow the whole life cycle.
A star is born 🌫️
Stars form from a **nebula** — a giant cloud of dust and gas. **Gravity** slowly pulls the cloud together, and as it collapses it heats up, forming a **protostar**. When the protostar gets hot and dense enough, something remarkable begins.
The main sequence ☀️
The core gets hot enough for **nuclear fusion**: hydrogen nuclei fuse into helium, releasing huge amounts of energy. The star is now a **main-sequence** star. It stays stable for **billions of years** because the **outward pressure** from fusion exactly balances the **inward pull of gravity**.
What holds a star up?
During its main-sequence life, what stops a star collapsing under its own gravity?
- The outward pressure from nuclear fusion in its core
- Its magnetic field
- The vacuum of space pushing inwards
- Nothing — it is slowly collapsing
Order the Sun's life
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It all depends on mass ⚖️
When a star runs low on hydrogen, it leaves the main sequence — and what happens next depends on its **mass**: • A star about the **size of the Sun** takes one path. • A star **much more massive** than the Sun takes a far more dramatic one.
A Sun-sized star 🔴
A star like the Sun swells into a **red giant**. It then throws off its outer layers, leaving a hot, dense core called a **white dwarf**. Over an enormous time the white dwarf cools and fades to a **black dwarf**. A calm, quiet ending.
A massive star 💥
A star far more massive than the Sun swells into a **red supergiant**, then dies in a colossal explosion — a **supernova**. What is left behind is either a **neutron star** or, for the very biggest stars, a **black hole**.
Match each stage to its description
- Nebula
- Main sequence
- White dwarf
- Supernova
- A cloud of gas and dust where stars form
- The stable phase, fusing hydrogen into helium
- The hot, dense remnant of a Sun-sized star
- The huge explosion of a massive star
What is a supernova?
Which best describes a supernova?
- A gigantic explosion at the end of a massive star's life
- The long, stable, hydrogen-fusing phase of a star
- The cloud of gas where stars are born
- A small, cool, dead star
What is left behind?
After a supernova, a very massive star leaves one of two remnants. Pick the TWO possible outcomes.
- A neutron star
- A black hole
- A white dwarf
- A brand-new nebula only
Order the massive star's death
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Star stuff ⚛️
Fusion in stars does not just make helium. Over a star's life it builds up heavier elements, up to **iron**. Elements **heavier than iron** are made in the extreme conditions of a **supernova**, which scatters them into space — the raw material for new stars, planets and, ultimately, us.
The life-cycle rules
A star spends most of its life on the _____ sequence, fusing hydrogen into helium. A star the size of the Sun ends as a white _____. A much more massive star explodes as a _____.