Stardust: Supernovae and Life -- The Cosmic Connection by John Gribben with Mary Gribben, Yale University Press, $24.95, 238 pages.



The Chapel Hill News


March 21, 2001

Twentieth-century discoveries teach us about our origins

By Phillip Manning

We -- you, me and everyone else on Earth -- are made out of stardust. This is not a figure of speech; it is literally true. In fact, every atom on Earth, the constituents of every rock and every river, came from the stars, except perhaps for a smattering of hydrogen and helium left over from the Big Bang. In his book "Stardust" (Yale University Press, $24.95), the British science writer John Gribben tells how scientists reached this startling conclusion.

For centuries, chemists have manipulated atoms, making the alloys and compounds that underpin our lives -- steel for cars, aspirin for headaches and plastics for almost everything. But where the atoms themselves, the building blocks of modern society, came from no one knew until recently.

The discovery of the source of atoms had to wait for three 20th-century scientific developments: the special theory of relativity, quantum mechanics and the Big Bang. In his Special Theory of Relativity, Albert Einstein postulated that mass could be converted into energy (and vice versa), an insight that is crucial to understanding how stars generate heat. Quantum mechanics enabled scientists to deduce how fundamental particles interact with one another inside a star. And the Big Bang gave physicists a starting point from which they could begin to solve the puzzle.

By the 1920s, scientists were starting to understand that our sun (like most, but not all, other stars) was made largely of hydrogen and helium. Then, in 1928, a brilliant young Russian physicist named George Gamow used the newly developing science of quantum mechanics to show how hydrogen nuclei could fuse together. This could happen only if the nuclei were moving at very high speeds, such as the nuclei in the intensely hot interior of an active star. By the late 1930s, physicists had figured out the chain of events that power the sun. Although the nuclear reactions are complicated, the net effect is that four hydrogen nuclei fuse together to form a helium nucleus. Some mass is lost in this process, and in accordance with Einstein's famous equation, E=mc2, energy is given off.

This energy keeps the sun at a toasty 15 million degrees Fahrenheit. Its heat warms the Earth and supplies the photons that kindle photosynthesis, the basis for life on our planet. One day the sun will completely convert its hydrogen nuclei to helium, and it will die. Fortunately for us, that day won't come for another 5 billion years, so you have time to finish your morning coffee. Nor will its death be a sudden one. When the sun has converted most of its hydrogen to helium, it will collapse and release gravitational energy, which will make it even hotter than it is today -- so hot that it will begin to burn helium. When three helium nuclei collide with sufficient force, carbon forms, and when a carbon nucleus meets a helium nucleus, oxygen is created.

So, from the hydrogen and helium produced in the Big Bang, our own sun will eventually create atoms of carbon and oxygen. Hydrogen, carbon and oxygen are three of the elements required for life. (Nitrogen, another element essential to life, is formed when slightly heavier stars than ours burn out and collapse.) Our sun will eventually use up its helium and shrink to become a white dwarf. Before that happens, though, some of the atoms that have formed in the sun's interior will be blasted into space in a final convulsion. In this stardust are the elements for a new generation of life.

But 92 elements occur naturally on Earth and throughout the universe, most of them heavier than carbon and oxygen and nitrogen. Where do they come from? The iron, the lead, the uranium? It turns out they come from the stars, too, but from bigger stars. Stars that are much more massive than Earth end their lives differently and far more spectacularly. Because they are heavier, they release even more gravitational energy when they collapse, and they get hot enough to fuse carbon nuclei. Heavier atoms form. Then nuclear fusion stops. Because heat is no longer being generated in the star's interior, it cools and collapses. This violent contraction creates a supernova, the most spectacular event in the universe.

In a fraction of a second, a supernova releases 100 times as much energy as our sun will generate in its entire 10-billion-year life. Temperatures climb to billions of degrees, and in this maelstrom, nuclei of all sorts fuse together, forming every known element. Then, an explosion so powerful that one can detect it across one-third of the observable universe scatters the newly formed elements into space.

When this stardust coalesces, new stars and planets form. You, me and the Earth itself were created from the recycled atoms formed in the stars of yesteryear. We are, indeed, children of the stars.

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