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Supernova and Supergiant Star Life Cycle

Learn about one of the biggest explosions known to humankind - a supernova. Follow a star's life cycle and learn how a star changes from a red giant to a supernova to a black hole or neutron star.


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One Of The Biggest Explosions Known


Diagram showing the life cycle of a star
Life Cycle of a Star


Supernova - one of the most explosive events known to humankind. Supernova explosions occur at the end of a star's life. Talk about going out with a bang!

A supernova is the ending of a star's life, but let's quickly explore the beginning.

Life Path Of A Star

Let's follow along the path of a star. A star is born in a solar nebula. As it grows, it enters one of two pathways of life. Depending on its size, the star becomes either an average star or a massive star. The average star then becomes a red giant, a planetary nebula, and ends its life as a white dwarf. The massive star turns into a red supergiant, goes supernova, and ends up as a neutron star or a black hole - again, depending on its size.

A star is born in a solar nebula and grows to adulthood as a main sequence star. Some stars end up much smaller than our sun and some much, much bigger. The way a star spends its later life and finally dies depends on how big it originally was. Small-to-medium stars turn into red giants, and big stars turn into red supergiants. These are some of the biggest stars in the universe by volume, although they are not the most massive. Betelgeuse and Antares are the best known examples of a red supergiant.

The creation of a supernova
Creation of a Supernova



Stars which are eight times or more massive than our sun - whether they are red giants or red supergiants - end their lives in a most spectacular way; they go supernova. A supernova is an explosion that occurs when the star runs out of fuel and fusion stops. Without the outward pressure from the fusion in the core there is nothing to counteract the inward pressure of gravity.

What happens first is that the outside of the star swells into a red supergiant. The core of the star begins shrinking and grows hotter and denser. For a while, a new series of nuclear reactions that turn the core to iron occur, which temporarily stops the collapse of the core - but it is only temporary.

When the core contains mostly iron, it has nothing left to fuse, and fusion in the core ceases.

In less than a second, the star begins the final phase of its collapse. The temperature in the core rises to over 100 billion degrees as the iron atoms are crushed together. There are a lot of forces going on at this point - some repulsive, some compressive - until finally the whole star explodes and produces a shock wave that forces the matter from the star into space.

A supernova can create either a small neutron star or a black hole
Neutron Star and Black Hole


All that remains of the original star is a small, super-dense core composed almost entirely of neutrons. This is a neutron star. If the original star was extremely big, even the neutrons don't survive, and the core collapses, forming a black hole.

Lesson Summary

A star starts in a stellar nebula and grows to a main sequence star (explored in another video). If the star grew big enough, it ages to a red giant, a huge star several times larger than our sun, in the later stages of its life. Eventually, the star dies in a huge explosion known as a supernova, a huge stellar explosion that is so big it can briefly outshine a whole galaxy.


The video below will help you understand how a supernova occurs.

Supernova Bounce Demonstration