“We’re made of starstuff.”
Carl Sagan’s famous quote underscores one of the most profound and fundamental facts of astronomy: the planets, stars and galaxies that appear so unimaginably far away from us are in fact connected to each living being on this pale blue dot by a vast and rich cosmic order.
A few minutes after the Big Bang, the explosion that created our universe, tiny particles called protons and neutrons joined together to form the first atomic nuclei, and soon the first atoms, mostly hydrogen and helium, but also small amounts of other stuff like deuterium (a heavier version of hydrogen) and lithium. It took perhaps hundreds of millions of years for these elements to fuse together in the cores of the first stars, which formed heavier elements such as the familiar carbon, nitrogen and oxygen.
Each subsequent generation of stars forged heavier elements than its predecessors, populating the universe with the hundred or so elements that we know occur naturally. Low-mass stars like our sun end their lives by gradually distributing their heavy elements into the surrounding interstellar medium (i.e. the space between the stars) by winds, forming beautiful objects called planetary nebulae. More massive stars end their lives by violent, brilliant explosions called supernovae which not only produce heavy metals like iron and copper, but also expel these elements to much larger distances. These explosions leave behind dense stellar corpses, either neutron stars, or the more popularly known, black holes.
As the Laser Interferometer Gravitational-Wave Observatory (LIGO) discoveries of the past decade have revealed, neutron stars and/or black holes can sometimes collide together to send ripples through space-time and in the process create some of the most precious metals known to humanity — gold, silver, platinum and so on. Therefore, when stars die, they disperse the heavy elements they form throughout their lives out to very far away. Today, we know that elements heavier than hydrogen and helium exist in significant amounts not just in the interstellar medium of all galaxies, but indeed beyond galaxies as well. These elements actually allow hydrogen gas to cool more easily, thus speeding up nuclear fusion in stellar cores, allowing stars to form more easily, which in turn forms more of these elements. And the whole cycle repeats.
Life on earth is believed to have emerged at least 3.5 billion years ago, but nobody knows whether it started from simple organic compounds already existing on earth or whether it was carried here from another place by meteoroids or space dust. What is clear though, is that the elements that make up the complex organic molecules present in all life on our planet (and that are found throughout our solar system) must have come from somewhere out in space. This is the grand cosmic connection: the calcium in our bones, the iron in our blood, the carbon, nitrogen and phosphorus in our DNA were all forged in the belly of a star eons ago.
The precious metals that humans have mined for thousands of years and that have laid the foundation for the earliest civilizations were produced in the devastating deaths of massive stars or perhaps the cataclysmic collisions of stellar carcasses ages ago. Humans, and all other life forms on earth, are intrinsically connected to distant reaches of space and time, despite being essentially stranded on a small rock orbiting an ordinary solitary star in some forgotten corner of the galaxy.
Our entire planet, everything we ever built, and even our physical bodies, bear the imprints of cosmic events so immense in scale and awesome in significance that they are almost impossible to fathom, even for people who spend their entire lives studying them. It is easy to think of yourself as insignificant or irrelevant in the vast ocean of space and time, but we are literally made of starstuff. We are the children of the cosmos, and in a way, we all come from outer space. And much like Carl Sagan declared decades ago, we are the cosmos knowing itself.
The mere action of you reading this article and pondering our origins in the cosmos is an example of the universe learning about itself. There is nothing insignificant about that.
Farhanul Hasan is a fourth year PhD student in the astronomy department at New Mexico State University, working on galaxy evolution and galaxy ecosystems. He can be reached at firstname.lastname@example.org.
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This article originally appeared on Las Cruces Sun-News: The elements that make you come from the stars