The burning hydrogen in the shell around the core significantly increases the brightness of the sun. The process of compression in the centre allows the outer regions of the star to expand outwards. As soon as the sun begins to burn more hydrogen, it would be considered a “red giant”.
But when the star has nothing left in the core to burn, gravitational forces take over.Įventually that force compresses the centre of the star to such a degree that it will start burning hydrogen in a small shell around the dead core, which is still full of helium. When the star has hydrogen to burn, the creation of helium produces enough outward pressure to balance out the gravitational pull. In a star, gravitational force pulls all the gases towards the centre. The trouble is that the sun’s core is not hot or dense enough to burn helium. Things change because the sun will have run out of hydrogen in its core – all that’s left is the helium. Even stars dieĪfter 8 billion years of happily burning hydrogen into helium are over, the sun’s life gets a little more interesting. Our solar system is just over 4.5 billion years old, so the sun is slightly more than halfway through its stable lifetime. For a star the size of ours, this phase lasts a little over 8 billion years. This means that it is in the most stable part of its life, converting the hydrogen present in its core into helium. The sun is currently classified as a “main sequence” star. After about a billion years the sun will become hot enough to boil our oceans. But the Earth will become uninhabitable much sooner than that. In a few billion years, the sun will become a red giant so large that it will engulf our planet.