You may fondly remember the classic Eighties science program Cosmos, narrated by the late great astrophysicist Carl Sagan. In the episode “The Shores of the Cosmic Ocean”, he famously uttered “we’re made of star stuff”. We are the products of nucleosynthesis, a set of processes that created the chemical elements, the building blocks of all we see and are.
Primordial nucleosynthesis arose with the Big Bang. In its fiery first moments, space was suffused with a roiling quantum plasma. Over the next 20 minutes, space expanded and the plasma cooled, precipitating hydrogen and helium. Over the next few billion years, these first elements accreted under gravity to form stars. About 98% of the observable universe is solely hydrogen and helium.
Nearly the remainder was born of stellar nucleosynthesis. Within the hearts of stars, thermonuclear reactions fuse hydrogen and helium atoms into more complex nuclei. On stellar winds, relatively light elements like carbon and oxygen are radiated into space, while heavier ones remain sequestered until stellar demise. Lightweight stars die gracefully, shedding iridescent nebulae containing elements like nitrogen, zirconium, and xenon. More massive stars cataclysmically self-destruct as supernovae, expelling metals like iron, copper, and nickel.
Often, supernovae leave behind remnant neutron stars. On occasion, these collide in a titanic event called a kilonova. Matter is instantly recombined into heavy elements like iridium, lead, and plutonium. Space-warping gravitational waves are also emanated, detectable from Earth. In August 2017, such a spectacle was witnessed for the first time. By most estimates, the kilonova synthesized ten Earth masses of gold and platinum. Other kilonovae have since been observed, via their intense gamma- and x-ray emissions.
Cosmic ray spallation is yet another form of nucleosynthesis, by which interstellar carbon, nitrogen, and oxygen are fragmented by radiation into lithium, beryllium, and boron. While a smidgen of these may have also precipitated from Big Bang cooling, and can be negligibly produced through stellar processes, spallation is thought to be the principal cause.
Interstellar elements eventually condense into new stars, renewing the cycle of nucleosynthesis. Around some stars form planets, setting the stage for life’s possibility. We are living proof of this.
In that Cosmos episode, Carl Sagan also said “We are a way for the cosmos to know itself”. Under one nucleosynthetic pedigree, we are equally heirs of the universe. In our conscious awareness, the universe marvels at its own existence.
You’ve been listening to Western Slopes Skies, produced by the Black Canyon Astronomical Society and KVNF Community Radio. This feature was written and voiced by Michael T. Williams.
