The Space & Beyond Blog
Life cycle of the sun
The Sun has been the center of our Solar System since the beginning of its existence. But, like everything else in the universe, the Sun has a life cycle.
How did the Sun form?
The life cycle of the Sun began roughly 4.6 billion years ago and will continue for almost another 8 billion years when it will have depleted its supply of nuclear fuel and collapse into a white dwarf. The Sun and all our planets in the solar system began as a giant cloud of molecular gas and dust. Then, about 4.5 billion years ago the cloud collapsed. From this collapse, dust and gas began to collect into denser regions. As the regions pulled in more matter, conservation of angular momentum caused it to begin rotating while increasing pressure caused it to heat up. Most of the material ended up in a ball at the center while the rest of the matter flattened out into a disk that circled around it. 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 temperatures and pressures in the interior ignited fusion at its core. And just a few million years later, it settled down into its current form. The life cycle of the Sun has now begun.
The Main Sequence Stage
Like most stars in our universe, the Sun is on the main sequence stage of its life. This means nuclear fusion reactions in its core fused hydrogen into helium. However, this process cannot last forever since there is a finite amount of hydrogen in the core of the Sun. Currently it has more than 72% hydrogen.
One billion years from now, the Sun will be 10% brighter than it currently is. This will trigger a moist greenhouse effect here on Earth that is similar to the hellish Venus environments that we see today. Under these conditions, life as we know it will be unable to survive anywhere on the surface of Earth.
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When will the Sun run out of fuel?
One day in the distant future the Sun will run out of hydrogen fuel. This will begin in approximately 6.4 billion years at which point the Sun will exit the main sequence stage of its life. With its hydrogen exhausted in the core, its inner helium ash that has built up there will become unstable and collapse under its own weight. The helium outside its core will start to fuse in a shell around the dead core. Then, our star will enter the red giant phase and swell up much faster. It is calculated that the expanding Sun will grow large enough to encompass the orbits of Mercury, Venus, and maybe even Earth.
Death of the Sun
All things must end. When people think of stars dying, what typically comes to mind are massive supernovas and the creation of black holes. However, this will not be the case with our Sun due to the fact that it is simply not massive enough. About one billion years after the Sun tries to swallow Earth, the red giant will undergo a process called Helium flash where huge amounts of Helium is fused to Carbon in a matter of minutes. Once the Helium in the core starts fusion, the star will then shrink but gain luminosity. Over the course of the next 20 million years, the Sun will then become unstable and begin losing mass through a series of thermal pulses. These powerful bursts of radiation will cause the Sun to fling wave after wave of material out into space. After about 500,000 years of these stellar tantrums, the Sun will have tossed away half of its mass. That discarded material will briefly form a beautiful planetary nebula. The remnant will eventually cool and become a white dwarf which is mostly made up of just carbon and oxygen. This smoldering ember will glow for trillions of years before fading to black.
Imagine being from another world, another civilization, far off in some other system like our own witnessing the Sun’s life cycle. It would look like so many mesmerizing stars and the stages that they go through, that we ourselves wonder and gaze upon. In the meantime, however, we have many days ahead of us filled with sunshine to look forward to. One thing is for sure, and that is that we must continue marching onwards because the universe, let alone the Sun, will not be slowing down for us to catch up.