The iron in your blood, the calcium in your bones, the oxygen in your lungs, and each one of the atoms that make up the material reality that surrounds you have been created at some point in the history of the universe. We are quite literally stardust, as most of the atoms in our body were created inside of stars, supernovae, and neutron star collisions.

The formation of chemical elements through nuclear fusion reactions in blazing stars is just one of the many ways the universe can generate the raw material that makes up all the worlds and forms of life. In this opportunity, we will explore the cosmological mechanisms of element formation.

Primordial nucleosynthesis

Immediately after the cosmic explosion that launched the universe we inhabit, processes that gave rise to the formation of the first atomic structures began to take place.

At 10 seconds old, the universe was small, tight, and boiling, and the fundamental particles that could exist were moving impetuously everywhere. Our entire world was more like an agitated hornet’s nest than the calm nocturnal ocean that today adorns our zenith.

The quarks and gluons constantly collided with each other, and radiation filtered through every little space, so during the first 20 minutes, only simple atoms composed of a single proton, neutron, and a modest electron in their orbit could be formed: hydrogen.

Since the universe was extremely hot and dense, it was an optimal setting for nuclear fusion. The agglomeration of the particles made it impossible for the heavier elements that formed to retain their structure, and they eventually decayed into lighter elements. Soon after, space expanded and cooled enough to make fusion impossible, leaving a distribution of 75 percent hydrogen, just under 25 percent helium, and a tiny amount of heavier elements such as lithium.

Stellar nucleosynthesis

For the next 500 million years, the universe was nothing but dispersed atoms and clouds of hydrogen and helium that gradually condensed to give rise to the first generation of stars.

These primordial stars were massive, so they used up their fuel quickly, compressing hydrogen into helium, helium into beryllium, beryllium into carbon, and so on. These fusions provide leftover thermal energy that keeps the star alive even before the iron is created. When the star’s core has enough iron, the gravitational pull it exerts disrupts the balance between the core’s gravity, which tends to squeeze and compact the star, and the radiation force, which pushes the top layers out. This imbalance leads the core to collapse in on itself, causing incredibly intense waves to propagate through the star’s outer layers and be blasted at high speeds into the surrounding space. This event is better known as a supernova.

The energy of the explosion is such that it is sufficient to generate the conditions of pressure and temperature that allow the synthesis of elements heavier than iron in very significant quantities. These spread through the interstellar medium to later form rocks, planets, and perhaps life.

Neutron star collisions

If something puzzled physicists and chemists for decades it is the origin of some heavy metals such as gold or platinum, since the energy they calculated a supernova explosion should have to generate them had never been observed. But even so, there is gold, so where does it come from?

There are few events in the universe much more energetic than the explosion of a star, and certainly, a pulsar merger is one of them.

When two neutron stars approach each other and become entangled in a gravitational dance with no escape and eventually collide, the energy of the event is so immense that it fuses heavy atomic nuclei, producing huge amounts of gold, among other metals in this range.

In fact, the number of pulsar collisions we’ve recorded, as well as their rate of gold production, are consistent with the amount of this metal present on our planet.

Other element formation mechanisms

There are other ways in which the universe forges other elements to supply itself and create new worlds such as white dwarf explosions and artificial synthesis, where the cosmos uses its most evolved form known—the human intellect—to create artificial materials in laboratories.

Isn’t it fascinating to think that the handful of gold atoms housed in our nervous system or the ring that adorns our finger come directly from the debris of an event as magnificent as the merger of two neutron stars? We are intimately related to all the processes that ever happened in the vast and unfathomable space that embraces us.