Why We're All Made Of Stardust | Unveiled

Why We’re All Made of Stardust

It was the famous astrophysicist Carl Sagan, a key figure for NASA and renowned as a driving force for popular science, who said in the 1980s that we’re all made of, what he called, “star stuff.” Since then, Sagan has been quoted far and wide, with his incredible assertion becoming a go-to fact for anyone with even a passing interest in physics! What’s even more impressive, though, is that it’s actually totally true! But what does it really mean?

This is Unveiled, and today we’re uncovering the extraordinary reasons why we really are all made of star stuff.

We know there are a certain number of chemical elements in the universe: these elements make up every single piece of matter in existence and they’re all made by a process called “nucleosynthesis”, which literally means to create nuclei, or atoms. The first elements were hydrogen and helium, made during the Big Bang when the universe was much hotter and more compact. It’s thought that this state only lasted for around twenty minutes, but during those twenty minutes at the dawn of time, the universe went from being literally nothing to becoming mostly hydrogen – seventy-five percent hydrogen, in fact. The rest was twenty-four percent helium and one percent “other stuff”, notably lithium. These are the three lightest chemical elements there are. The first stars were formed from them… and it was in those stars that the process of “stellar nucleosynthesis” began, and that heavier elements were created. Today, most of what appears on the periodic table can be (and has been) made inside of stars.

This ability that the universe has, to create heavier and heavier elements as time goes on, is called “galactic chemical evolution”. Heavy elements - like iron, for example - need to be fused, inside stars, from lighter, more abundant elements like hydrogen and helium. And if we trace it back far enough, we can see a cosmological chain of development for everything in existence. The first stars produced the first heavier elements… and then the next generation of stars used those elements to make more variations… and so on, and so on. It’s a process which is actually set to continue indefinitely, until the ultimate end of the universe… meaning that, as time goes on, newer, heavier elements will be created in other, younger stars.

And it’s not as though it’s something which is totally out of our hands, either. Humans are able to replicate the conditions inside of stars through nuclear fusion here on Earth, to create new elements for ourselves. Four additions to the periodic table (made official in 2016) were created this way - nihonium, moscovium, tennessine, and oganesson. What’s an incredible thought, though, is that, in a few billion years’ time, the necessary ingredients for life itself might have completely changed from what they are now… lifeforms in the distant future could well be based on currently new, synthetic chemical elements like these, or even on something else entirely - something that we don’t presently have a hope of synthesizing on Earth. Some scientists take the idea even further, and have gone so far as to suggest that (as well as Earth’s spatial “habitable zone” around the sun) we currently live in a “temporal” habitable zone as well, because it’s also thanks to the chemical, elemental conditions of today that we (in our current state) can exist in the universe right now. We have all the elements we need to grow and live in abundance at this point in time exactly because the galactic chemical evolution is at just the right stage.

But, while that’s all pretty incredible in itself, how is it that these elements, created by stars, find their way into us in the first place? Well, primarily it’s down to supernovae. Supernovae - usually seen as massive explosions from a dying star - are bright and spectacular but they also aren’t all that common. In fact, they’re one of the rarest ways for a star to die, because it’s only the most massive stars which are able to go out with such a bang. An even smaller number of massive stars collapse into black holes (where they pull stuff in rather than blast it out) but, even so, supernovae are a crucial reason why reality - including our existence - is the way it is. A supernova blasts all the rare elements that have been fused inside its particular stellar core out into space… scattering all of its physical properties far and wide. And, eventually, gravity takes hold so that these elements can be made into new things: new stars, but also new planets, asteroids, and even organisms. It’s because of this that some of the elements inside you - inside all humans - technically date all the way back to the moment of the Big Bang, 13.8 billion years ago. And after humans die and the sun expands and the Earth is one day destroyed, those same elements will find their way back into other stars and planets, perhaps ready to begin the cycle of creation again.

Such a “rebirth” scenario is arguably even more likely when you consider that most of the chemical elements that exist aren’t necessary for life as we know it. In fact, there are only six elements essential for life on Earth: carbon, hydrogen, nitrogen, oxygen, phosphorus, and sulfur. While we might use other elements for other not quite so essential processes (as well as things like construction and technology), these are the fundamental ones that we need to live, and which make up all other forms of life on Earth – plants, animals, microbes, and so on. And the most exciting thing of all is that none of these elements are unique to this world; they exist everywhere, meaning that, theoretically, there really could be life on other planets that functions in much the same way as we do. Or, at least, there could one day be life on other planets elementally similar to us.

All planets could have access to the same base materials, depending on what’s available at any one time in any one place. We know that there are billions of potentially habitable planets (at least, spatially habitable) in just our own galaxy. But, like Earth, they also exist in (or close to) a temporal habitable zone, as well. The existence of life is still the product of an incredible coming together of all the necessary elements (plus billions of years of evolution), but if it’s happened once… couldn’t it happen again? For some scientists, it’s crazier to think that life wouldn’t grow in other places when the universe seems to widely distribute all the requisite ingredients to create a world.

We haven’t yet travelled to any other stars to measure and record their composition at closer quarters, but one experiment which has helped us to understand their elemental makeup (and their significance to our own creation) is the Apache Point Observatory Galactic Evolution Experiment, carried out across the 2010s by the Sloan Digital Sky Survey. It used a spectrograph to examine distant objects, translating the wavelengths of light emitted from them to calculate and quantify the elements that contribute to any given star’s existence. And, while it’s true that elements exist in different quantities and ratios inside a star compared to inside a human being, it’s also true that traces of humanity - and the building blocks of life on Earth - can be found all across the cosmos.

All of the elements that go into creating a human being were originally formed in the hearts of distant stars, potentially millions of lightyears away, and some even came from the Big Bang itself. And that’s why we are all made of star stuff.