The Sun is expected to “burn out” or exhaust its nuclear fuel in about 5 billion years. Currently, the Sun is in the middle of its life cycle, undergoing a stable phase known as the “main sequence,” during which it fuses hydrogen into helium in its core, producing energy and light.
What Happens Next?
1. Main Sequence (Current Phase): The Sun has been in this phase for about 4.6 billion years and will continue for another 5 billion years or so. During this time, it steadily converts hydrogen into helium.
2. Red Giant Phase: When the hydrogen in the core is depleted, the Sun will start to fuse hydrogen in a shell around the core, causing the outer layers to expand and the Sun to grow into a red giant. It will swell to a size where it could engulf the inner planets, possibly including Earth.
3. Helium Burning: In the red giant phase, the core will become hot enough to fuse helium into heavier elements like carbon and oxygen.
4. Planetary Nebula and White Dwarf: Eventually, the Sun will shed its outer layers, forming a planetary nebula. The core will then contract into a white dwarf—a small, dense remnant about the size of Earth. This white dwarf will gradually cool and fade over billions of years.
While life on Earth would not survive the red giant phase, the Sun’s complete “burnout” as a white dwarf will take place over a very long timescale, with the fading process extending for tens of billions of years.
