As of now, we know that there are 92 elements found in nature and 283 variants, commonly referred to as isotopes.
But which element was created first?
A recent international study led by Professor Alexander Heger from the School of Physics and Astronomy at Monash University, published in Nature, reveals that calcium may be the heaviest element formed in the first stars.
A photo capturing Mount Can Bin shielding the JUNA laboratory from cosmic radiation. Superimposed is a stylized fireball representing a nuclear collision. The image of the Milky Way with ancient stars in the night sky was taken by the James Webb Space Telescope. (Image source: JianJun He)
Theoretically, previous studies had identified calcium, but this is the first study to confirm its production and formation process in the first generations of massive stars.
Professor Heger stated that this research significantly contributes to enhancing the community’s understanding of the chemical evolution of the universe.
“The nature of the first-generation stars— the largest and oldest stars— remains one of the most intriguing open questions in astrophysics,” Professor Heger shared.
“Our study describes for the first time how most of the calcium is produced: through the slow boiling of the hydrogen burning process rather than through supernova explosions.”
When the hydrogen burning process in the star’s core is completed, hydrogen continues in the shell while the helium core undergoes nuclear fusion reactions to create diverse changes.
Most material beneath the helium core typically disappears in models of large stars. The expelled material undergoes thermodynamic reactions and many other reactions. The hydrogen burning process in the shell is usually hotter, less dense, and occurs faster than the hydrogen burning process in the core.
To analyze the full range of these effects and the modification rates affecting the conclusions, the researchers conducted full model calculations for a 40 M star of primordial composition. They used the KEPLER hypothesis, a fully coupled adaptive nuclear reaction network, to meticulously track the evolutionary process and atomic synthesis.
The study highlights the importance of investigating nuclear reactions within the carbon-nitrogen-oxygen (CNO) cycle (enhanced) to understand the atomic synthesis processes of the first-generation stars and relies on observational data to draw unique conclusions about the nature of those stars in the early universe.
Inside the star with the least iron content, SMSS0313-6708, a notable signature of calcium was observed, but iron could not be detected, even though it is an element commonly produced by supernovae alongside calcium.
“Experts often consider calcium to be a direct descendant of the first stars in the universe, formed from the leftover material after the Big Bang,” Professor Heger explained.
“The ultra-metal-poor UMP star has a very high lifespan, and what we can see about its composition is like a time capsule from before the first galaxies formed. This discovery is a remarkable contribution to the exciting observational processes that will be conducted by the James Webb Telescope in the near future.”
