We are all made of stardust....

Prof. Dr. Karl-Heinz Kampert on the coming and going of stars and the origin of our existence.

Where do humans come from? Regardless of questions of faith, scientists worldwide have been investigating the origin of our existence for many years. The magic word is: stardust. But where does it come from, how does it develop and above all, what does it have to do with our life? The Wuppertal astrophysicist Prof. Dr. Karl-Heinz Kampert explains it with the processes in the universe, in which no atom is ever lost.

Elements that make life possible

Mainly, a human being consists of water and oxygen. The rest are metals and non-metals. But scientifically correct, we evolved from stardust. "It always sounds so metaphorical. 'We were created from stardust`!' But it's actually true," says Prof. Dr. Karl-Heinz Kampert, who heads the astroparticle physics department at Bergische Universität. "The elements that build us, i.e. hydrogen, oxygen, carbon, nitrogen, these are, after all, the essential elements that made life possible. Also, everything heavy that is in us, calcium, magnesium, iron, all of that has been created in stars and stellar explosions throughout the history of the universe. Without that, we wouldn't exist."

First-generation stars

Gaseous giants, the first stars, formed from the hydrogen and helium gas clouds created in the Big Bang through attractive forces.

"In the first three minutes after the Big Bang, the light elements were formed, that is, hydrogen and helium, as well as extremely small traces of lithium, beryllium and boron," Kampert explains, "which, however, did not yet contain the preconditions for life. After this fulminant explosion, the scientist continues, there first came an epoch in which the universe had to cool down again. The gas clouds clumped together and the first stars formed. "That happened some 100 million years later, much shorter than we thought twenty years ago. Then the first hydrogen-rich stars formed, and they mostly had relatively short lifetimes."

When Kampert talks about time spans, he is usually talking about millions or even billions of years. A short stellar lifetime, he said, spans between 10 and 50 million years. "The sun, for comparison, has an approximate lifetime of nine billion years," but is also already a second- or third-generation star, he said, because it already contains fragments of heavy elements. "Of course, it still consists essentially of hydrogen and helium, but there are also already the heavy elements, which shows that the sun was created from the remains of earlier stellar explosions. And from that, eventually, the Earth was created."

Cooking pots of the universe with countless stars

Heavy elements, then, contain the building blocks of life and are found only in second- or third-generation stars. "Stars are the cooking pots of the universe," Kampert says with a laugh, "in which heavy elements are first created. And when such a cooking pot boils over, you can compare it to a supernova explosion. Then, for a short time, large amounts of heavy elements are created explosively, which is what makes us human." A galaxy has about 100 billion stars, he said, and there are also as many galaxies in the universe, so the number of stars is unimaginably high.

Planetary nebula condenses into new stars

The remains of a so-called Supernova form together with star shell and erbrüteten elements a dust nebula from larger and smaller objects up to macroscopic dust particles, which waft by the universe and produce sometime also new celestial bodies. The sun is a typical star, Kampert explains, that inflates at the end of its life to form what is known as a planetary nebula, as many stars before it have done. "But there are also stars with much greater mass than the sun, with 30 to 50 or even 100 solar masses, that end up as apocalyptic supernovae instead." The process is always the same, he said. In the inside of a star hydrogen would be burned like a function engine first to helium. But because of the abundance of mass, the gravitational pressure from outside on the inner "furnace" is so high, he said, that it has to burn much faster and hotter to withstand the outside pressure. "This depletes the energy supply very quickly, and the star lives for a shorter time, though we're still talking about 10 to 50 million years." The eternal fire thus burns gradually with hydrogen first fusing to helium, which then continues to carbon, nitrogen, oxygen, silicon, etc., until iron is created at the end of this chain. "With iron, the combustion process then stops. When the iron core, i.e., the inner ash of the star, finally reaches a mass corresponding to more than one and a half solar masses, then the iron core can no longer stabilize and collapses, becoming a neutron star." This process would momentarily release a great many neutrons, which would be captured in the star's remaining envelope, where they would give rise to the heavy elements that make up life. "It's a constant coming and going, a circular economy in the universe."

The building blocks of the human body have a long journey behind them

At some point, you get to humans via these many metamorphoses. About half of all the atoms on Earth, and thus the building blocks of every human body, have already made a long journey through the far reaches of space. "That's actually the case," the physicist explains, "every atomic nucleus in us, except for hydrogen, which comes from the Big Bang, has had that long journey." Exploded stars, often multiple supernovae in parallel or in short intervals of the first generation after the Big Bang, would have spewed dust into the cosmos. "That's when large formations are created in interstellar space, lots of magnetic fields are created, and everything gets jumbled up," Kampert recounts. After a period of cooling, gravity causes the elements to reassemble, forming new stars, and the process repeats. Although the universe is already about 14 billion years old, there are still stars of the first generation. However, he said, they are very light, which allows them to burn the nuclear fusion furnace inside very sparingly.

"... Dust to dust."

Nearly every atom in the human body was once part of a star. That can be a comforting notion even beyond death, assuming that matter is always being created anew. "I think it's a beautiful notion, too, because that's how we came to be. Also, this formula - without becoming religious - 'earth to earth, ashes to ashes, and dust to dust`, has existed before, even before one became aware of these processes, and it is physically completely correct." Two papers were written in 1957 that formulated this insight, Kampert reports. "At that time, it was understood for the first time that all these heavy elements that make us up were created in stellar explosions and stars. And ultimately, that's where we humans came from."

No atom is ever lost: recycling in space as a model?

Not a single atom in space is ever lost. From what was, what is and what will be, new matter is created in the eternal cycle of becoming, decaying and becoming new. Everything is recycled and returned to the cycle of nature as building material. Kampert says: "That is absolutely right. No atom is ever lost, everything is recycled and again and again new stars and and also new life arise from it. Nature impressively demonstrates this to us." The problem with us humans, he said, is unfortunately that we behave as if there are endless resources. "Of course, you can say we're just converting. But locally on planet Earth, this leads to the fact that we are currently burning more, i.e. releasing energy, than new energy can be stored. Coal, oil and gas were created millions of years ago and were stored in the earth by nature. Today, they are released again within a very short time. And as a result, the climate gets out of sync and what we're observing happens." Martin Rees, court astronomer to the late Queen Elizabeth II and professor of cosmology and astrophysics at Britain's Cambridge University, says, "Humans are stellar nuclear waste." This is not very flattering, but seen in this way, we could only emerge through many stellar recycling processes, and that means a constant sustainability in the evolution of the universe, from which we on Earth are still far away. "The realization that nature recycles everything," Kampert concludes, "should give us food for thought."

Uwe Blass

Prof. Dr. Karl-Heinz Kampert studied physics at the Westfälische Wilhelms-Universität Münster from 1977 to 1983. From 1983 to 1986, Kampert was a research assistant at Westfälische Wilhelms-Universität, earning his doctorate in 1986. He then spent three years as a postdoctoral research fellow at the major research facility CERN in Switzerland. From 1989 to 1995, he was an assistant professor of physics at Münster University, during which time he habilitated in 1993. He then taught as a professor of physics at the University of Karlsruhe and the Karlsruhe Research Center, both of which merged to form the Karlsruhe Institute of Technology in 2009. Finally, since 2003, he has been teaching experimental physics at the University of Wuppertal.