Are We Really Made of Stardust?

Saying that we are made of stardust sounds poetic, but behind that statement is pure science. Everything you see around you was once a part of some star.

When the Universe was young, it was made of hydrogen and helium atoms. Today, these two are still responsible for over 98% of the Universe’s mass, but the heavier elements were created in stars. Have in mind that we are only talking about “normal” matter in the Universe. Dark energy and dark matter are responsible for over 95% of its mass. The remaining 4.6% is made of 98% hydrogen and helium and 2% all heavier elements together.

This implies that the first generation of stars did not have planets orbiting them, except maybe gas giants made purely of hydrogen and helium, but without enough mass to ignite like stars do. What happened in those first stars and is still happening in stars today is the stellar nucleosynthesis, the process where lighter elements fuse into heavier elements with the help of gravity pressuring them together and the weak interaction turning protons into neutrons.

When stars start running out of hydrogen to turn into helium, at their core they start producing heavier elements from their helium supply. Then, after some time, they start creating even heavier elements and so on. This process ends when chemical element iron is created and the star has run out of fuel. Less massive stars will deplete their fuel before their core becomes iron, but the point is that all elements up to and including iron are created in stars in nucleosynthesis. All elements heavier than iron are produced in a couple of moments after the very massive star with an iron core has collapsed under its own weight. This is what we call supernova and the creation of elements during this process is supernova nucleosynthesis.

Human body is made mostly of elements lighter than iron. By mass, we are made of 65% oxygen, 18% carbon and 10% hydrogen and 7% other elements. There is no helium atoms in human body. This means that 90% of your body was made of elements that never even existed before the first generation of stars created them. So yes, we are made of stardust.

Even more interesting, some of the atoms inside our bodies were made in supernova explosions that happened billions of years ago. Either way, we are all to the great extent made of stardust. If that is too poetic to you, you could say we are made of stars long dead.

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