Every single atom around us, including those in our own bodies, originated in momentous cosmic events that predate the Earth.
We know this because there are only a limited number of ways to create them, which means that the atoms that are us once came from places like the center of a star.
Our Sun is what astronomers call a ‘third generation’ star. It and its planets (including the Earth) formed from the remnants of at least two earlier generations of stars.
But the story really begins minutes after the Big Bang. The early universe was full of searing heat and pressure, where trillions of free-floating protons and neutrons fused together to form the first hydrogen and helium atoms. As the universe cooled over the next few million years, they formed enormous gas clouds, from which galaxies and the first stars were made.
Even now, billions of years after the Big Bang, most of the matter in the universe is that original hydrogen and helium.
Hydrogen and helium are like building blocks because these two elements, combined and rearranged, have formed every other element. Each one has a slightly different origin story, and the creation of these other elements is called ‘nucleosynthesis’.
Stars are almost always involved in nucleosynthesis. They are born within clouds of gas and dust in space, where gravity pulls the cloud into a dense ball.
Stars are usually responsible for the creation of new elements
When this ball reaches a certain mass, its internal pressure becomes strong enough to fuse atoms like hydrogen and helium together. At this point the star ignites and starts to shine.
This gives off a huge amount of heat and light, and the hydrogen and helium turns into other elements like iron, nitrogen, and oxygen which are the star’s waste products.
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After billions of years the star will run out of hydrogen and helium, and the waste elements build up. What happens next depends on how massive the star is.
Dying and exploding stars
Stars with 8x the mass of our Sun and smaller are considered to be ‘low mass’ stars. When they die they create a massive explosion called a ‘planetary nebulae’. The blast seeds space with particles of lithium, carbon, nitrogen, and other elements in smaller amounts. Scientists are certain that at least 21% of the atoms in our bodies were created in this way.
The core of low mass stars typically survive the explosion. It continues to shine despite having shed much of its mass, though it’s small and not very bright. We call these stars ‘white dwarves’.
Stars with more than 8x the mass of the Sun are considered ‘massive’ stars. They tend to blow up in an even bigger explosion called a ‘supernova’. A supernova is one of the most immense and powerful phenomena in the universe. If the Sun went supernova, it would be 1,000,000,000 times brighter on Earth than a hydrogen bomb pressed against your eyeball.
It is a cosmic event so powerful and prodigious that we have no frame of reference with which to really understand it. Supernovae are visible across entire galaxies and we can see one every few years as a temporary ‘extra’ star in the night sky.
In the explosion the contents of the star are expelled into space, and the force of the blast fuses it’s atoms to create a vast array of elements. Supernovae give us oxygen, sodium, neon, aluminium, and many more. At least 65% of the atoms in our bodies originate in a supernova.
I feel that statistics like these are among the most incredible in all of science. Who could have predicted that the matter that makes up us is actually star stuff, and the true history of what we are involves such stunning cosmic events.
Massive stars leave behind a tiny ultra-dense core called a ‘neutron star’, compressed by the force of the explosion.
Exploding white dwarves
Many star systems contain two or more stars closely orbiting each other, in addition to their asteroids and planets. These are called ‘binary’ star systems, and if one star is a low mass star, it can create a special type of supernova explosion.
When the low mass star explodes and becomes a white dwarf, it can steal mass from its companion star. If it grows large enough (past the mass of 1.4x our Sun) it will explode all over again in a ‘Type Ia supernova’. This is a unique environment that creates titanium, manganese, nickel, and zinc.
Events like this may seem rare and unlikely, but our galaxy alone contains hundreds of billions of stars; enough for even the most unlikely events to become nearly inevitable.
Merging neutron stars
If two companion stars are both massive stars, when they collapse into neutron stars they may collide. They will be crushed together into an even bigger neutron star, and sometimes into a black hole.
When this happens, spectacularly intense conditions are produced. A magnetic field trillions of times stronger than the Earth’s is created in two to three milliseconds, the gravitational pull is enormous, and a slew of rare elements are fused in the surrounding gas like uranium, plutonium, and gold. More than 90% of all gold was produced through an incredible event like this.
Cosmic ray fission
When supernovae explode or when neutron stars merge, they emit a form of highly intense electromagnetic radiation into space.
They travel at the speed of light and when they encounter something – like a dusty cloud of atoms like carbon, nitrogen, or oxygen, they will collide with them and cleave them in two. From these collisions, we get beryllium, boron, and lithium.
Some atoms (especially big ones) are too unstable to last long in nature. Over periods of time ranging from seconds to millions of years, they emit radiation and decay into smaller elements. We’ve created a number of elements like this, sometimes on purpose and sometimes as waste products of nuclear bombs, nuclear energy, and particle accelerators.
These elements include technetium, used in diagnosing bone cancer, and californium, used in nuclear reactors. Some of these synthetic elements will last for millions of years, and are almost guaranteed to be the final artifacts of human civilisation. How they got to Earth
Our Sun, the planets, and everything on them were formed in just the right place inside of a dusty nebulae, where the remnants of all of these cosmic events were mixed together. Over time they were pulled together by a centre of gravity which became our Sun and the solar system.
On one of those planets, a special type of chemistry called ‘life‘ discovered how to repurpose these atoms into an enormous variety of incredible forms, giving rise to the natural world. The origin of our atoms is just one small part of the story of the universe, which is the most detailed and astonishing creation story ever conceived.