Topic 8 - space physics

Question 1

describe the full life cycle of a star

Answer 1

1. stars initially form a cloudof dust and gas called a nebula
2. 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 eachother. when the temperature gets high enough , hydrogen nuclei undergo nuclear fusion to form helium nuclei. this gives out huge amounts of energy which keeps the core of the star hot , a star is born .
3. the star enters a long stable period wherethe outward pressure that tries to expand the star balances the force of gravity pulling everything inwards. in this stable period its called a main sequence star and typically lasts several billions of years.
4. eventually , the hydrogen runs out . the star then swells into a red giant (if its a small star ) or a red super giant (if its a large star) . it becomes red becasue the surface cools. fusion of helium occurs. heavier elements up to iron are created in the core of the star.
5. a small to medium sized star like the sun then becomes unstable and ejects its outer layer of dust and gas. this leaves behind a hot dense solid core - a white dwarf
6. as a white dwarf cools down . it emits less and less energy . when it no longer emits a significant amount, it is called a black dwarf .
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