Chinese scientists have revealed the origin of calcium in first stars by using the world's deepest underground laboratory in southwest China's Sichuan Province, according to a study published online Wednesday in the journal Nature.

In 2014, Australian astronomers observed the oldest star ever known by human beings, a K-type red giant star named SMSS0313-6708, on which lithium, carbon, magnesium and calcium were observed. However, the origin of calcium in the star remained a mystery.

The Standard Model of Cosmology assumes that the universe began 13.8 billion years ago with a Big Bang. The first stars and galaxies burst into existence somewhere at the end of the "Dark Ages," which is about 380,000 to 150 million years after the Big Bang, said He Jianjun of Beijing Normal University, the first corresponding author of the article.

The China Jinping Underground Laboratory (CJPL), which is 2,400 meters under a mountain in southwest China's Sichuan Province, started operating in December 2010.

Chinese researchers carried out relevant experiments in the laboratory. They successfully verified the hypothesis that calcium comes from a key breakout reaction of carbon, nitrogen and oxygen cycle, revealing the origin of calcium in the star.

The CJPL can reduce the influence of cosmic rays and provide unique conditions for direct measurement of important nuclear reactions of astrophysical interest, said He.

Reviewers of the journal Nature commented that the study is a great experimental success, and that it provides a new insight for future nuclear astrophysics studies.   

(With input from Xinhua)