We are all made of stardust. It sounds like a line from a poem, but there is some solid science behind this statement. Almost every element on Earth was formed at the heart of a star.
Did you ever wonder where you came from? That is the stuff that’s inside your body like your bones, organs, muscles…etc. All of these things are made of various molecules and atoms. But where did these little ingredients come from? And how were they made? The answer to these questions will take us back to a time long ago when the universe was much different than it is now. However, the physics was the same.
Stars are formed when clouds of dust and gas particles coagulate (come together) to form bigger masses. When the mass gets big enough, the resulting gravity fuses these particles together, which generates a lot of heat and radiation. At some point, the mass gets big enough to where a star is formed.
Over its lifetime, a star sustains this nuclear reaction - called a fusion reaction - which fuses smaller hydrogen and helium atoms together to form heavier elements. Toward the end of its life, the star begins running out of smaller atoms to fuse together and the fusion reactions slow down. This results in cooling that causes the core to contract, while the outer layer expands out.
Eventually, the outer layer collapses in on the core and the resulting heat this generates causes the star to explode in what's called a super nova. And, the force of this explosion causes heavier elements to be formed and blown away from the star in a nebula of particles (the heaviest element to occur naturally is uranium). Much of the core stays intact to become what's called a black dwarf (small star that's not burning any more), a neutron star (all of the atoms collapse in on each other as one mass of protons and neutrons), or a black hole, depending on the initial mass of the star.
In the mean time, the expelled heavier particles then roam the universe until they're picked up by other stars or they come together to form bodies of heavy elements (like asteroids or even planets). And, since human life developed on a planet that was formed of materials that could only have been developed by the super nova death of a star, which was originally generated by dust and gases called stardust (also know as star stuff), humans are essentially made of stardust.
Next time you’re out gazing at stars twinkling in the night sky, spare a thought for the tumultuous reactions they play host to. It’s easy to forget that stars owe their light to the energy released by nuclear fusion reactions at their cores. These are the very same reactions which created chemical elements like carbon or iron - the building blocks which make up the world around us.
After the Big Bang, tiny particles bound together to form hydrogen and helium. As time went on, young stars formed when clouds of gas and dust gathered under the effect of gravity, heating up as they became denser. At the stars’ cores, bathed in temperatures of over 10 million degrees C, hydrogen and then helium nuclei fused to form heavier elements. A reaction known as nucleosynthesis.
This reaction continues in stars today as lighter elements are converted into heavier ones. Relatively young stars like our Sun convert hydrogen to produce helium, just like the first stars of our universe. Once they run out of hydrogen, they begin to transform helium into beryllium and carbon. As these heavier nuclei are produced, they too are burnt inside stars to synthesise heavier and heavier elements. Different sized stars play host to different fusion reactions, eventually forming everything from oxygen to iron.
During a supernova, when a massive star explodes at the end of its life, the resulting high energy environment enables the creation of some of the heaviest elements including iron and nickel. The explosion also disperses the different elements across the universe, scattering the stardust which now makes up planets including Earth.