Stellar Evolution: Life Cycles of Stars
Stars are born, live and die over billions of years, and a star's mass decides its fate. Follow the life cycles of a Sun-like star and a giant, from nebula to white dwarf, neutron star or black hole.
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The lives of the stars ⭐
Stars are not fixed and unchanging. Like living things, they are **born**, they shine for millions or billions of years, and eventually they **die**. What happens at the end depends almost entirely on one thing: the star's **mass**. This module follows the life cycles of a Sun-like star and a much more massive star.
Words for a star's life 🔑
Four ideas run through this topic:
A balancing act ⚖️
A star stays stable because two forces are in balance. **Gravity** pulls its material **inward**, while the **radiation pressure** from nuclear **fusion** in the core pushes **outward**. While these balance, the star sits on the **main sequence**. When the core fuel runs low, fusion slows, gravity wins for a time, and the star begins to change.
What holds a star up? 🎯
On the main sequence, what balances the inward pull of gravity?
- The outward radiation pressure from nuclear fusion
- The star spinning quickly on its axis
- The gravitational pull of nearby planets
- The magnetic field of the galaxy
Two very different endings 🌟
A star's mass decides its fate. A Sun-like star ends quietly; a much more massive star ends in a violent explosion.
Life of a Sun-like star 🪜
An interactive activity.
A massive star's life ✅
Select the TWO stages that belong to a MUCH MORE MASSIVE star's life cycle.
- Red supergiant
- Supernova
- Planetary nebula
- White dwarf
Match the remnant 🔗
- White dwarf
- Neutron star
- Black hole
- Black dwarf
- The dense remnant of a Sun-like star, held up by electron pressure
- The remnant of a massive star, held up by neutron pressure
- Forms when the most massive cores collapse and not even light escapes
- What a white dwarf becomes once it has cooled and stopped glowing
Degeneracy pressure and a limit 💫
When fusion stops, what holds a stellar remnant up? In a **white dwarf** it is **electron pressure**; in a **neutron star** it is **neutron pressure**. But electron pressure has a limit. The **Chandrasekhar Limit**, about **1.4 solar masses**, is the greatest mass a white dwarf can have. Above it, electron pressure fails and the core collapses further, into a neutron star or a black hole.
The Chandrasekhar Limit 🔢
An interactive activity.
The life of a star in words 🧩
A star is born in a _____ of gas and dust and spends most of its life on the _____ sequence, fusing hydrogen. A Sun-like star then swells into a _____ giant. A much more massive star ends its life by exploding as a _____. The dense remnant left by a Sun-like star is a white _____.
Naming the stars 🌌
In the Bayer naming system, what does the name Alpha Centauri tell you?
- It is a bright star in the constellation Centaurus
- It is the tenth object listed in a catalogue
- It is a planet orbiting the Sun
- It is the distance to the star in light years
Evidence for black holes 🕳️
An interactive activity.
Follow a star's fate 🧭
An interactive activity.
Compare two lives ✍️
An interactive activity.