Asked by: Leslie Griffin, Malvern
Stars die because they exhaust their nuclear fuel. The events at the end of a star’s life depend on its mass. Really massive stars use up their hydrogen fuel quickly, but are hot enough to fuse heavier elements such as helium and carbon. Once there is no fuel left, the star collapses and the outer layers explode as a ‘supernova’. What’s left over after a supernova explosion is a ‘neutron star’ – the collapsed core of the star – or, if there’s sufficient mass, a black hole.
Average-sized stars (up to about 1.4 times the mass of the Sun) will die less dramatically. As their hydrogen is used up, they swell to become red giants, fusing helium in their cores, before shedding their outer layers, often forming a ‘planetary nebula’. The star’s core remains as a ‘white dwarf’, which cools off over billions of years.
The tiniest stars, known as ‘red dwarfs’, burn their nuclear fuel so slowly that they might live to be 100 billion years old – much older than the current age of the Universe.
Subscribe to BBC Focus magazine for fascinating new Q&As every month and follow @sciencefocusQA on Twitter for your daily dose of fun science facts.