The Sun’s Lifespan

Today we’re going to do a deep investigation into the life of one of your favorite stars: the Sun! The incredible star-power of the Sun holds our solar system together and makes life on Earth possible with its warmth and light. What makes our sun work, and how long does it plan to stay in business? Let’s go behind-the-scenes to find out!

How did the Sun come to be? This radiant fireball is the result of changes 4.6 billion years ago to a massive molecular cloud in space. Scientists have found evidence that a giant cloud composed mostly of hydrogen and helium underwent a dramatic shift, possibly instigated by nearby supernova explosions. In response to dramatic outside forces, the molecular cloud collapsed and compressed into stars, including our own Sun.

As the cloud compressed into stars, different chemical phenomena began to occur that gave the Sun its form and shaped its course in the galaxy. As parts of the cloud collapsed, they would begin to rotate, consolidating mass into the center. Much like our planet Earth, the central core began to heat up. Our Sun is a gaseous object formed around a heated core of hydrogen and helium where fusion is constantly occurring.

Right now, we are approximately halfway through the phase called the “Main Sequence” of our Sun. The Main Sequence is where the Sun burns the hydrogen and helium at its core, releasing that energy into our solar system. Eventually, the Sun’s supply of these elements will be exhausted and the Main Sequence will come to an end, but that lies approximately 5.4 billion years in the future.

At the core, fusion is causing the center of the Sun to become denser, even as it burns. As the Sun burns it increases very gradually in brightness and size. Our sun is growing about 1% brighter every 100 million years it burns. The size of the Sun is also increasing very gradually during this phase of the Sun’s life.

The Sun’s bright future is going to be a bit too bright for human comfort. While the Sun is currently fusing hydrogen into helium and releasing energy into space, eventually it will run out of things to burn in its core.

When the Sun runs out of the elements fueling its reaction it begins the final stages of its life. In about 5.4 billion years the Sun will run out of hydrogen to burn, although it will still have helium at its core. During this phase of its life, the Sun will expand and brighten as it becomes a red giant. Once core hydrogen is depleted, the sun will double in size and brightness over the course of 500,000 years. Then the next 500,000 years will see it expand much more rapidly, increasing to 200 times its current size, a radius that will engulf Mercury, Venus and even our dear Earth.

This very large Sun will also be 1000 times brighter than it is today, although the temperature of this Red Giant will be comparable to our current Sun. After brightening and expanding, it is anticipated that the remaining helium in the core will ignite and within mere minutes much of the core will be formed into carbon and the expanded mass will rapidly condense.

The star then begins to cool while it goes through an unstable phase of condensing and ejecting mass. Because our Sun is not hot enough to explode in a supernova, it will instead go through a period of thermal pulsing where its size and brightness will vary immensely. Eventually, the Sun will be reduced to a core, a White Dwarf that will contain about 54% of the Sun’s current mass, the rest of its mass dispersed into the cosmos as a planetary nebula. The White Dwarf stage of our Sun’s life will be its longest, lasting for trillions of years before finally fading from the sky.

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