Why might the sun run out of energy?

Question: Why might the sun run out of energy?
- Keywords:
  energy,
  gas,
  sun
Asked by to Dave on 13 Jun 2014. This question was also asked by , , , .
- Dave Jones answered on 13 Jun 2014:
  
  The Sun shines because in its centre it is burning Hydrogen (turning it into Helium). When it doesn’t have any more Hydrogen left in its centre to burn (because it has already burnt it all), that will mean it has run out of fuel and can’t burn anymore. I’m interested in what happens after that!

Question: Why might the sun run out of energy?