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The Life Cycle of a Star

Updated on September 9, 2017

Life cycle of a star

Early life

A star will form from a cloud of dust and gas in space gravity pulls these together. As it does it becomes hot once it is hot enough it will start to fuse hydrogen together to form helium. This is called fusion this process will release energy that keeps the core of the star hot this is called the main sequence. During a star's main sequence of its life, it is stable because the forces are balanced In the star. Depending on the size of the star is how long this main stage is. For a big star, it is quite short as it burns through its fuel quickly, it might only last a few million years. A small star like our sun will burn for about 10 billion years because it uses its fuel more slowly.

End of life a small star

After the main stage depending on the size of a star there are two processes that will happen. For a small star like our sun when the hydrogen fuel runs out the core will contract under the weight of its own gravity. But some hydrogen fusion will happen in the upper layers of the star as the core is contracting it heats up. This heats the upper layers of the star causing the upper layers to expand. As they expand the star will get bigger making the star a Red giant. The core will be now hot enough to make helium fuse into carbon. After about 1 billion years the fuel runs out and the star starts to shrink until the new helium shell reaches the core. The helium ignites and the layers of the star are blown off in a cloud and dust called a planetary nebula. As the core continues to collapse in on itself it eventually becomes a white dwarf.

End of life a big star

A big star like a small star when it runs out of hydrogen it begins to fuse helium into carbon. (it expands as well because a large star is already large it don't become a red giant it becomes a red supergiant.) But once the helium is gone the star's big mass is enough to fuse the carbon into heavier elements like oxygen and magnesium. But once the core has turned into iron it can no longer burn and the star collapses from its own gravity. The core turns into a neutron core after the outward layers of the star fall on the core causing it to crush the core. The core heats up to billions of degrees and then explodes. This is called a supernova and this releases a lot of energy into space. The remains of a big star either become a neutron star or a black hole.



Nuclear fusion

Nuclear fusion involves two nuclei reacting together to make a larger nucleus this releases a lot of energy. This is the process that happens in the Sun. The Sun does this by fusing two Hydrogen atoms together to form Helium.

Fusion on Earth

Nuclear fusion is a great way of creating energy and would be very useful on Earth. We can see what happens in the Sun every day and clearly the sun gives off a lot of energy in the form of heat. But there is a problem with controlling it because it only happens in very hot conditions like in the Sun. We can create these condition on Earth but that kind of high temperature needs to be contained because it will cause damage to anything around it. Unfortunately, we have no material that can contain that kind of heat so we can not do nuclear fusion. Although there would be no problem getting the Hydrogen isotopes for the process because the ocean can provide it as water is made up of Hydrogen and Oxygen. (1.)


1. Nuclear fusion. Retrieved from:

© 2017 Astro


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