A team of scientists has peered into stellar interiors, revealing the chaotic forge where chemical elements form. The Big Bang 13.8 billion years ago produced most light atoms during the first three minutes, especially hydrogen. Stellar cores fuse hydrogen into heavier elements, creating layered shells that culminate in iron at the center. Silicon- and sulfur-rich layers lie deep beneath other materials and are normally inaccessible to direct observation. In September 2021 a telescope recorded the spectrum of supernova SN 2021yfj, located 2.2 billion light-years away, capturing a rare opportunity to probe those inner layers.
The nitrogen in our DNA, the calcium in our teeth, the iron in our blood, the carbon in our apple pies were made in the interiors of collapsing stars. We are made of starstuff, proclaimed American astrophysicist Carl Sagan in his famous book Cosmos almost half a century ago. A team of scientists has now been able to peer into these stellar bowels for the first time, the chaotic forge where the chemical elements that make up human beings and everything around them are formed.
I was dazzled, recalls German astrophysicist Steve Schulze, who led the research. To understand the significance of this discovery, we must go back to the Big Bang that gave rise to the universe 13.8 billion years ago. In the first three minutes after the Big Bang, almost all of the universe's light atoms were formed, especially the ever-present hydrogen, the accumulations of which form stars.
In the interior of a star, the temperature and pressure are so high that hydrogen fuses and forms increasingly heavier elements, starting with helium. The combination of silicon and sulfur, for example, produces iron, the heaviest atom that can be generated inside a star. The result is a kind of cosmic onion, a term commonly used by astronomers. This process transforms the star into a layered structure: hydrogen on the outside, then helium, then layers of carbon/oxygen, magnesium/neon/oxygen, oxygen/silicon/sulfur, and finally iron in the center.
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