Stars, galaxies and the Big Bang

Stars are born in clouds of gas and dust, shine by fusing hydrogen into helium for billions of years, and end in different ways depending on their mass. Light from distant galaxies tells us the universe is expanding.

Key facts

  • Life cycle: nebula → protostar → main sequence → red giant (or supergiant) → white dwarf, or supernova → neutron star or black hole.
  • Our Sun will become a red giant then a white dwarf.
  • Red shift: light from distant galaxies is stretched to longer wavelengths; further galaxies are more red-shifted.
  • Red shift and the cosmic microwave background support the Big Bang theory.

Worked examples

Example 1

What evidence shows the universe is expanding?

  1. Light from distant galaxies is shifted towards red: they’re moving away.
  2. More distant galaxies move away faster, so space itself is expanding.

Answer: Red shift