Life of the Sun | Universe Today

Written by Fraser Cain

The Sun we enjoy today; the one that warms our planet with life giving energy, it just one stage in the life of a typical star. The sun looked different in the distant past, and it will become terrifying and unrecognizable in the future. But this is all just the life of the Sun.

Solar Nebula
The Sun (and all the planets) started its life as a giant cloud of cold molecular gas and dust. Something bumped into the cloud, like the gravity from a passing star, or shockwaves from a supernova. This caused the cloud to collapse. With the collapse, the mutual gravity from the particles in the cloud pulled together, and formed pockets of denser material in the cloud. These were star forming regions, and one of them was to become the Solar System.

Protostar
As the cloud collapsed, conservation of momentum for all the particles in the cloud made it start spinning. Most of the material ended up in a ball at the center, but this was surrounded by a flattened disk of material. The ball at the center would eventually form the Sun, while the disk of material would form the planets. The Sun spent about 100,000 years as a collapsing protostar before temperature and pressures at the core ignited fusion at its core. The Sun started as a T Tauri star – a wildly active star that blasted out an intense solar wind. And then, just a few million years later, it settled down into its current form. The life of the Sun had begun.

Main Sequence
The Sun, like most stars in the Universe, is on the main sequence stage of life. It converts 600 million tons of hydrogen every second into helium, generating a tremendous amount of solar radiation. For the Sun, this process got going 4.5 billion years ago, and it has been generating energy this way every since. But there isn't an unlimited amount of hydrogen in the core of the Sun. In fact, it's only got another 7 billion years worth of fuel left. As the Sun creates more helium at its core, the Sun burns a little more hydrogen. This causes the output of the Sun to go up. You won't notice it now, but in about a billion years, the output from the Sun will have increased by 10%. This will be enough to boil the oceans into water vapor. This water vapor will escape into space, and the Earth will resemble Venus. Needless to say, life on Earth will have a difficult time surviving. The life of the Sun will last in the main sequence phase for about 12 billion years.

Red Giant
Like I said above, the Sun will eventually run out of hydrogen in its core. When this happens, the Sun will switch to burning helium instead, creating carbon, nitrogen and oxygen. This will cause the Sun to increase in size a tremendous amount. It's expanding size will consume Mercury and Venus, and probably even Earth. And the amount of energy coming from the Sun will increase many times over. This period will only last a few hundred million years. And then, the Sun will sputter a few times, releasing its outer layers into space. The life of the Sun will be nearly over.

White Dwarf
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. This will mark the end of the life of the Sun.

We have written many articles about the life of the Sun for Universe Today. Here's an article that looks at a white dwarf as an example of the future of our Sun.

Would you like to know about the life of the Sun in great detail? This article has one of the best descriptions of each phase of the Sun's life.

We have recorded an episode of Astronomy Cast just about the Sun called The Sun, Spots and All.

Filed under: Astronomy