The Sun became a star about 4.5 billion years ago, when it started to fuse hydrogen into helium in its core. Astronomers have estimated that the star with the mass of the Sun has enough hydrogen to maintain stable fusion reactions over 10 billion years. After that the core will become mostly helium, the Sun will become unstable, it will swell and become a red giant. Eventually it will expel its upper layers that will form a planetary nebula and its core will collapse into a white dwarf.

How long before the Sun will exhaust hydrogen in its core and become a red giant?