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The Death of the Sun

All things must end. That’s true for us, that’s true for the Earth, and that’s true for the Sun. It’s not going to happen tomorrow, but one day in the far future, the Sun will run out of fuel and end its life as a main sequence star and die.

In about 6 billion years, the Sun’s core will run out of hydrogen. When this happens, the inert helium ash built up in the core will become unstable and collapse under its own weight. This will cause the core to heat up and get denser. The Sun will grow in size and enter the red giant phase of its evolution. The expanding Sun will consume the orbits of Mercury and Venus, and probably gobble up the Earth as well. Even if the Earth survives, the intense heat from the red sun will scorch our planet and make it completely impossible for life to survive.

When Will the Sun Burn Out?

Once it has become a red giant, the Sun’s death is just around the corner. It’ll still have enough heat and pressure at its core to begin a second stage of fusion, burning helium this time to form carbon. This phase will last for about 100 million years until this source of fuel is exhausted. Finally, the shell of helium becomes unstable causing the Sun to pulse violently. It will blow off a large fraction of its atmosphere into space over the course of several pulses.

When the Sun has blasted off its outer layers, all that will remain will be central core of carbon. In fact, it will be an Earth sized diamond with the mass of a star. This is a white dwarf, and it will still be hot enough to shine with thermal radiation. But it’s no longer generating solar fusion, and so it will slowly cool down until it becomes the same temperature as the rest of the Universe; just a few degrees above absolute zero. This will take about a trillion years to happen.

The Sun’s death will be complete.

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