Chapter 8 - Astrophysics

Question 1

Describe the lifecycle of a star of a similar mass to our sun.

Answer 1

Stars initially form from a cloud of dust and gas called a nebula. The force of gravity pulls the nebula together to form a protostar. When the temperature gets high enough, hydrogen nuclei undergo nuclear fission to form helium nuclei. This produces a huge amount of energy. The star enters a period of stability, usually lasting a few billion years (the more massive it is, the shorter this time will be) over this time the outwards pressure caused by thermal expansion will balance the force of gravity meaning gravity pulls everything inwards. Eventually its hydrogen core runs out and the star is compressed enough to become a red giant. The red giant sheds its outer layer of dust and gas leaving the dense core, called a white dwarf.

Question 2

Describe the lifecycle of a star of a larger mass than our sun.

Answer 2

Stars initially form from a cloud of dust and gas called a nebula. The force of gravity pulls the nebula together to form a protostar. When the temperature gets high enough, hydrogen nuclei undergo nuclear fission to form helium nuclei. This produces a huge amount of energy. The star enters a period of stability, usually lasting a few billion years (the more massive it is, the shorter this time will be) over this time the outwards pressure caused by thermal expansion will balance the force of gravity meaning gravity pulls everything inwards. Bigger stars start to glow brilliantly as they undergo fusion to make metals heavier than iron. They expand and contract several times then explode in a supernova. This ejects the cloud of dust and gas to leave either a black hole or neutron star depending on the star’s mass.