Supernova: Definition & Explanation

Instructor: Richard Cardenas

Richard Cardenas has taught Physics for 15 years. He has a Ph.D. in Physics with a focus on Biological Physics.

In this lesson you will learn the definition of a supernova and what conditions are necessary for a star to become a supernova. You will also learn what happens to the star after the supernova.


Ever wonder what happens to a star when it dies? Not all stars die in the same way. The death of a star depends on what kind of star it was in the first place. Any star with the same mass and size of our sun will expand and become red giants, then they eject their outer layers, and the remaining core becomes a white dwarf or a black dwarf. When the star is much larger and heavier than our sun, something more dramatic happens to the star when it dies. These stars will also expand like our sun, but because of their size, the star will shed its outer layer in a large explosion called a supernova. In a supernova, the star heats up to billions of degrees and dies in a large fiery explosion, which releases large amounts of energy and matter into space.

How a Star Becomes a Supernova

To understand how a star dies, we must understand how a star lives. When a star is young, it is mostly made up of hydrogen and some helium. A process called nuclear fusion provides the energy that fuels the star. Simply put, when two atoms collide at such high speeds, they form a new kind of atom. When the atoms are very light, like hydrogen and helium, energy is released. The star contains such a large amount of hydrogen and helium colliding at high speeds, that this is enough energy to fuel the star.

The process of hydrogen fusion yields helium. When the hydrogen runs out, the star combines helium to form carbon. If the mass of the star is large enough, the carbon atoms can be fused to form heavier atoms all the way up the periodic table to iron. Once the star is made up of iron, it can no longer burn. The gravity of the large star causes the iron to collapse upon the small core of the star. In the process of collapsing, the iron core heats up. The outer layers of iron collapsing upon the small iron core cause the core to compress even further. This process causes the core to heat up to billions of degrees, which causes a massive explosion. In this explosion, the star ejects matter and energy into space. This explosion is called a supernova.

The interesting thing is that this explosion can trigger the formation of new stars. Also, the core that remains can have two fates: become a neutron star or a black hole depending on the size of the original star. If the star was originally about at least 10 times larger than our sun, it will die and become a neutron star. Stars with masses over 20 times the mass of the sun may eventually become black holes. Our sun will die a very quiet death and become either a white dwarf or a black dwarf.

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