1
Q
How does a main sequence star form?
A
- Stars initially form from a cloud of dust and gas called a nebula
- The force of gravity pulls the dust and gas together to form a protostar. The temperature rises as the star gets denser and more particles collide with each other. When hot enough, nuclear fusion occurs with hydrogen nuclei forming helium nuclei.
- The star is now in a long stable period where the outward pressure caused by nuclear fusion balances the force of gravity pulling everything inwards
2
Q
What happens to a small star when hydrogen runs out?
A
- It swells into a red giant because the surface cools. Heavier elements are created in the core
- The star then becomes unstable and ejects it s outer layer of dust and gas, leaving behind a hot, dense sold core - a white dwarf
- As as white dwarf cools, it emits less and less energy until it becomes a black dwarf
3
Q
What happens to a large star when hydrogen runs out?
A
- The stars glow brightly and expand and contract several times. Eventually, they explode in a supernova, ejecting heavy elements which forms new planets and stars
- The exploding supernova throws the outer layers of dust and gas into space, leaving a very dense core called a neutron star. If a star is massive enough, it will become a black hole
4
Q
What is the big bang theory?
A
The theory that all matter in the universe occupied a very small space which was very dense and very hot. It then exploded and space started expanding
5
Q
What is red-shift?
A
Light from distant galaxies are shifted towards the red end of the spectrum, suggesting the source of light is moving away from us. The greater the red-shift, the faster the galaxies are moving away
