“The nitrogen in our DNA, the calcium in our teeth, the iron in our blood, the carbon in our apple pies were made in the interiors of collapsing stars. We are made of starstuff.” — Carl Sagan
That man knew how to make connections. A couple weeks back, we looked at how hydrogen atoms are squeezed together in the center of the sun and fuse to form helium, a new element. Just to refresh, an element is a substance made of atoms with the same number of protons. Hydrogen always has one proton in its nucleus; carbon always has six and gold always has 79.
If you remove one proton from a gold atom’s nucleus, it becomes platinum. If you add a proton, it becomes mercury. Adding and subtracting protons takes vasts amount of energy and modern particle accelerators, the reason the alchemists of old couldn’t possibly succeed in transforming lead into gold.
But do stars make all the elements? Let’s start by looking at what we’re made from. Nearly 99% of the mass of your body consists of just six chemical elements: oxygen, carbon, hydrogen, nitrogen, calcium, and phosphorus in order of most to least. Another five elements — potassium, sodium, sulfur, magnesium and chlorine — make up most of the remaining 1%. Hydrogen and helium are the simplest elements; to make the more complicated ones, we have to dial up the pressure and heat.
As the sun ages, the helium created by hydrogen fusion settles in its core, becomes more compressed and ultimately gets hot enough to “burn”. That won’t happen for another 6 billion years give or take. On that distant day, helium nuclei will fuse to form carbon. In a side process, some of the carbon fuses with helium to create oxygen, which has 8 protons in its nucleus.
So now we have helium, carbon and oxygen. Helium doesn’t react with much, so you won’t find any in your body, but carbon and oxygen (bound up in water as H2O, bones and more) are plentiful. Question is — how do those elements get out of sun-like stars and into outer space, where they can be recycled into a new generation of stars and planets, and in the lucky case of Earth, living things?
Due to nuclear reactions in its core, as a sun-like star ages, it produces additional heavy elements such as nitrogen by combining simpler elements in the presence of catalysts like carbon. Consider that all the stars we see were born from dust and gas seeded from earlier generations of stars, which spent their lives cooking up elements, too. Smidges of carbon, nitrogen, lead and many other elements are incorporated in every new flight of stars including our sun.
As stars age, their cores become extremely hot through compression, while the rest of their bulk bloats into a huge, tomato-colored windbag called a red giant star. Within the core, simpler elements capture neutrons (neutral particles in atoms) and in a fascinating bit of nuclear alchemy, the neutrons transform into protons, releasing energy in the process. As the protons get heaped together, yet more complex elements are created including copper, zinc, silver, titanium, sodium and others.
An aging red giants develops powerful winds that blow its outer envelope — everything but the blazingly-hot core — into outer space in a beautiful bubble of glowing gas called a planetary nebula. Finally, all the goodies painstakingly assembled over 10+ billion years of evolution, are spewed into space and available to re-collect and build new stars and planets. All that had to happen to get make your body and provide the materials for your home and car.
Stars born much more massive than the sun have the required heat and pressure to cook up elements beyond carbon and oxygen. Supergiant stars fuse carbon to make neon (yes, the same gas in neon signs); neon fuses to make oxygen; oxygen fuses to create silicon and silicon fuses to make iron. Once a star accumulates iron in its core, it reaches the end of the line for element creation through fusion. Iron can’t be fused to make heavier elements; instead, the extra heat breaks iron apart into lighter elements. With no heat from fusion in the supergiant’s core to counteract the pull of gravity, the star collapses, rebounds and explodes as a supernova. Not only does this release all those elements into space, but the tremendous heat during the collapse and detonation bombards the cooked-up elements inside the star with lots and lots of neutrons, creating gold, platinum, uranium, plutonium and many others.
Added all together, stars create every single element found in nature except for the two most abundant: hydrogen and helium. Where or where did they come from? That’s easy. The Big Bang! Approximately 73% of the mass of the visible universe is hydrogen with helium making up about 25%. Everything else comes to just 2%. The universe started out way too hot for atoms to form, but 3 minutes after the Big Bang, the temperature of space had cooled enough for first hydrogen atoms to form (single protons) followed by helium and a very small amount of lithium. After that, it was too cool for additional elements to assemble. We had to wait for the first and subsequent generations of stars to take these simple materials and transform them into the world we know today.
Remember I said earlier that just six elements comprised 99% of your body? Since the average male adult body is about 57% water and water is composed of two hydrogens for every oxygen, 67% of that water is hydrogen. That makes hydrogen atoms the most abundant of all the elements in your body. Every single one of them is about 15 billion years old, birthed in the Big Bang and on loan for the duration of our lives until surrendered at death to re-use for another purpose.
We are but momentary creations giving voice to the elements or as Carl Sagan said: “We are a way for the cosmos to know itself.”