Are we made of stardust?

Our planetary scientist, Dr Ashley King explains how, because of this spectacular phenomenon, we might actually be made of stardust.

The first generation of stars

Elements are matter that can’t be broken down into simpler substances. On the periodic table, each element is distinguished by its atomic number, which describes the number of protons in the nuclei of its atoms.

We think that the universe began about 13.8 billion years ago with the Big Bang. At that point, only the lightest elements, such as hydrogen, helium and minuscule amounts of lithium existed.

The first generation of stars formed as lumps of gas drew together and began to combust. This caused a nuclear reaction in the centre of a star. The first stars that formed after the Big Bang were greater than 50 times the size of our Sun.

“Inside stars a process takes place called nucleosynthesis, which is basically the making of elements,” Ashley says. “The bigger the star, the faster they burn their fuel.”

The first stars burned their fuel quickly and were able to make only a few elements heavier than hydrogen and helium. When those stars went supernova, they expelled the elements they had produced and seeded the next generation of stars.

The next generation of seeded stars were then able to produce other, heavier elements such as carbon, magnesium and nearly every element in the periodic table. Any element in your body that’s heavier than iron has travelled through at least one supernova.

“It’s very likely that there are a whole bunch of different stars that have contributed the elements we see in our own solar system, our planet and those found within you", explains Ashley.

“It’s totally 100% true – nearly all the elements in the human body were made in a star and many have come through several supernovas.”

The life cycle of a star

The burning that takes place inside stars draws on a huge amount of fuel and creates an enormous amount of energy.

“Stars are immense objects – over 99% of the mass in our solar system is in our Sun – and gravity squeezes them. Meanwhile, the burning inside a star creates energy which counteracts the squeeze of gravity which is why our Sun is stable.”

Stars stay in this equilibrium with gravity until they run out of fuel. “When that happens to really big stars you can get some really, really spectacular supernovas,” Ashley says. “Our own Sun won't be anywhere near as dramatic as that.”

When stars die and lose their mass, all the elements that had been generated inside are swept out into space. The next generation of stars form from those elements, burn and the elements are swept out again.

Ashley says, “This constant reprocessing of everything is called galactic chemical evolution. Every element was made in a star and if you combine those elements in different ways, you can make species of gas, minerals, and bigger things like asteroids. From asteroids you can start making planets and then you start to make water and other ingredients required for life and then, eventually, us."

“This process has been going on for something like 13 billion years and our solar system is thought to have formed only 4.5 billion years ago.”

Looking back in time through space

Large stars last for a few million years, while smaller stars last for more than 10 billion years.

“You can’t really watch a star form and see what happens in real time. When you look at the stars through a telescope what you’re seeing probably happened millions of years ago,” Ashley explains. “You can tell some things about their make-up based on colour and temperature, but not everything.”

Scientists can tell the temperature and age of stars from their colour. Hotter stars burn blue, while cooler and older stars burn red.

“In 1987, there was a supernova that actually made it possible for scientists to watch and record a ring of material being ejected, but this kind of occurrence is rare.”

What is stardust made of?

The other way to study the life cycle of stars is by  finding samples of cosmic dust and observing them through an electron microscope.

Invisible to the human eye, a single speck of this very pure, original stardust is only a few microns in size – 100 times smaller than the width of a human hair. They’re known as pre-solar grains, because they’re older than our Sun.

“We find it in the really, really pristine, primitive meteorites that were never altered on asteroids in the early solar system,” Ashley explains. “It’s like looking for a needle in a whole field of haystacks.”

To find pre-solar grains, scientists take a tiny chip of a primitive meteorite and dissolve 99.9999% of it until they’re left with a residue of silicon carbide, graphite and nanodiamonds. As things that are made at high temperatures in the atmosphere of stars are resistant to acid, this matter is left behind.

To find out more about space and our relationship with what lies beyond our planet, visit our exhibition – Space: Could Life Exist Beyond Earth.