How a star forms from a nebula, why a main sequence star is stable, the two ways a star ends, and where elements are made.
What you will learn
- Put the stages in the life of a star in order, for a Sun-sized star and a much more massive one
- Explain the balance of forces in a main sequence star
- Say where elements up to iron, and heavier than iron, are made
How a star is born
Every star starts the same way.
- a nebula, a huge cloud of dust and gas, is pulled together by gravity
- it becomes a protostar: squeezed tighter, it gets hotter and hotter
- when it is hot and dense enough, hydrogen nuclei fuse into helium nuclei, releasing energy
- it is now a main sequence star, and stays stable for millions to billions of years
On the main sequence two effects are in equilibrium: gravity pulls the star's material inwards, and the energy from fusion produces a pressure pushing outwards. They balance, so the star keeps a steady size. The Sun has been like this for about 4.6 billion years.
The rest of this lesson and its 9 practice questions are locked.
In this lesson
- How a star is born
- Two ways to end
- Where the elements come from
- Try it: Name the stage
9 practice questions, marked as you go; about 25 minutes in all.
Key terms
Mass, Red giant, White dwarf, Red supergiant, Supernova, Neutron star, Black hole, Iron, Heavier than iron, Supernovae
In this unit: Space physics
The solar system and the Milky Way, the life cycle of a star, orbits and orbital speed, red-shift and the expanding universe, and what is still unknown.