Stars are formed from clouds of dust and gas collapsing under gravity. They spend most of their life fusing hydrogen into helium in their cores, glowing from the heat and pressure of nuclear fusion. When stars run out of fuel to burn in their cores, they die - smaller stars may become white dwarfs, while larger stars explode as supernovae. The material from exploded stars then disperses to form new dust clouds, starting the next generation of star formation.