Fate of the Sun

The sun has been shining for about 4.5 billion years. It has enough hydrogen fuel to "burn" for about 10 billion years. The size of the sun is a balance between the outward pressure made by the release of energy from nuclear fusion and the inward pull of gravity. When the core runs out of hydrogen fuel, it will contract under the weight of gravity; however, some hydrogen fusion will occur in the upper layers. As the core contracts, it heats up and this heats the upper layers causing them to expand. As the outer layers expand, the radius of the sun will increase and it will become a red giant. The radius of the red giant sun will be just beyond the Earth's orbit, so the Earth will plunge into the core of the red giant sun and be vaporized. At some point after this, the core will become hot enough to cause the helium to fuse into carbon. When the helium fuel has exhausted, the core will expand and cool. The upper layers will expand and eject material. Finally, the core will cool into a white dwarf and then eventually into a black dwarf. This entire process will take a few billion years.

As you can see, our sun is quite complex and interesting, and now you know more about how it produces the light and heat that all life on Earth depends on.

For more information about the sun and related topics, check out the links on the next page.