Nuclear fusion scientists uncover ancient star mysteries in an underground lab

Astronomers have long sought to directly observe stars categorized under the title of "population III". These population III stars are believed to have formed up to 250 million years after the Big Bang. Astronomers have never observed these stars directly — most are thought to have exploded as supernovae eons ago — though they do believe they have spotted stars that came into existence in the aftermath of a population III star's destruction.

One example comes in the form of a star called SMSS0313-6708 that is 13.6 billion years old, making it one of the oldest stars ever observed. The star, located only 6,000 light years from Earth, has mystified scientists due to the fact it has a higher concentration of the element calcium than is expected in such an old star.

The world's deepest operational nuclear physics laboratory

In a bid to shed new light on this mystery, Zhang and his team set out to mimic a nuclear reaction that enables ancient stars to produce heavier elements, including calcium.

They carried out their experiments inside the China Jinping Underground Laboratory (CJPL), which is comprised of a subterranean tunnel some 2,400 meters deep under a mountainside. It is the deepest operational laboratory for particle and nuclear physics experiments in the world.

The underground facility shields experiments from cosmic radiation that reaches the Earth's surface and, above ground, would mess with the incredibly precise instruments required for the nuclear fusion experiments. Nuclear fusion is the reaction by which the sun produces energy — it's a reaction many scientists are trying to harness in a bid to create a commercially viable method for producing practically limitless energy.

'The nuclear forges of the cosmos'

Zhang and his team discovered that a specific reaction — that produces a version of the element neon — likely occurred 7.4 times more often in ancient stars than previously thought. The reaction explains the high calcium content of SMSS0313-6708. The team's study also explains that their results provide more accurate measurements for this "crucial reaction", which have previously been "inaccessible in aboveground laboratories."

"SMSS0313-6708 is an ultra-metal-poor star that is speculated to be a direct descendant of the first generation of stars in the Universe that formed after the Big Bang,” Zhang's team explained in their study. "The observable composition of an ultra-metal-poor star is a time capsule to the environment before the first galaxies formed — complementing the exciting upcoming observations of the James Webb Space Telescope, which is now aiming to give a first look at the earliest stars and galaxies."

The team's efforts, carried out deep underground, highlight the wide-ranging implications of reactions in the very oldest stars, as they essentially act as "the nuclear forges of the cosmos, responsible for the creation of most elements heavier than helium in the Universe," the researchers explained.