What does the inside of a carbon atom look like? A recent study from the Jülich Research Center, Michigan State University and the University of Bonn provides the first comprehensive answer to this question. A breakthrough study has revealed the internal structure of the carbon nucleus, highlighting the importance of the Hoyle state and providing new insights into the arrangement of nuclear particles. This research paves the way for further discoveries in nuclear physics.

The neutrons and protons in the carbon nucleus are three atomic groups composed of four neutrons and four protons. Depending on the energy state of the nucleus, these neutrons and protons can be arranged into an equilateral triangle (left) or into slightly curved arms (right). Image source: Professor Serdar Elhatisari/University of Bonn

In this study, the researchers simulated all known energy states of the atomic nucleus. That includes the baffling Hoyle status. If the Hoyle state did not exist, carbon and oxygen would have minimal presence in the universe. Therefore, we also owe our existence to it. The research was published in the journal Nature Communications.

Composition and dynamics of atomic nuclei

The nucleus of a carbon atom usually consists of six protons and six neutrons. But how exactly are they arranged? When atomic nuclei are bombarded with high-energy radiation, how do their configurations change? The scientific community has been searching for answers to these questions for decades. Especially because they could provide an answer to a mystery that has long puzzled physicists: Why are there so many carbon atoms in space — without which there would be no life on Earth? After all, shortly after the Big Bang, there was only hydrogen and helium. The hydrogen nucleus consists of one proton, and the helium nucleus consists of two protons and two neutrons. All heavier elements were created billions of years later by aging stars. In these stars, helium cores fuse into carbon cores under tremendous pressure and extremely high temperatures. This requires three helium nuclei to fuse together.

Professor Dr. Ulf Meißner from the Helmholtz Institute of Radiation and Nuclear Physics at the University of Bonn and the Institute for Advanced Simulation at Forschungszentrum Jülich explained: "But in fact this is unlikely to happen. Why? The energy of helium nuclei is much higher than that of carbon nuclei."

However, that doesn't mean they're particularly easy to blend, quite the opposite: it's like three people trying to jump on a merry-go-round. But since they run much faster than a merry-go-round, it's difficult to succeed.

Hoyle state: key to carbon formation

Therefore, as early as the 1950s, British astronomer Fred Hoyle speculated that three helium nuclei first came together to form a transition state. This "Hoyle state" is very similar to the energy of a helium nucleus. It's like a merry-go-round that spins faster so three passengers can easily hop on. When this happens, the carousel slows down to normal speed.

"Only by bypassing the Hoyle state can stars create appreciable amounts of carbon," said Meissner, a member of the interdisciplinary research area "Modeling" and "Matter" at the University of Bonn.

Advanced simulation technology

About ten years ago, together with colleagues from the United States, Forschungszentrum Jülich and Ruhr-Universität Bochum, he successfully simulated the Hoyle state for the first time.

"At that time we already knew how the protons and neutrons of the carbon nucleus were arranged in this state. However, we could not prove with certainty that this hypothesis was correct," he explains.

With the help of an advanced method, researchers have now succeeded. This is mainly based on constraints: In reality, protons and neutrons - nucleons - can be located anywhere in space. However, to perform their calculations, the research team restricted this degree of freedom: "We arranged the nuclear particles at the nodes of a three-dimensional lattice," explains Meißner. "Therefore, we only allow them to be in certain strictly defined positions. It is precisely because of this restriction that it is possible to calculate the movement of nucleons. This task is very complicated because the interaction between nuclear particles differs depending on the distance."

The researchers also ran millions of simulations with slightly different starting conditions. This allowed them to see where protons and neutrons were most likely to appear.

"We performed calculations for all known energy states of the carbon nucleus," says Meißner. The calculations were performed on the JEWELS supercomputer at the Jülich Research Center. In total, the calculations required about 5 million processor hours, with thousands of processors working simultaneously.

reveal the structure of the atomic nucleus

These results effectively provide an image of the carbon nucleus. They prove that nuclear particles do not exist independently. "Instead, they cluster into groups of two neutrons and two protons," the physicist explains. This means that three helium nuclei can still be detected after they have fused to form a carbon nucleus. Depending on the energy state, they exist in different spatial forms - either arranged in an isosceles triangle, or like a slightly bent arm, with one core each at the shoulder, elbow and wrist. "

This study not only gives researchers a better understanding of the physics of carbon nuclei. "The method we developed can easily be used to simulate other atomic nuclei and will certainly lead to completely new insights," Meissner said.

References Shen Shihang, Serdar Elhatisari, Timo A. Lähde, Dean Lee, Bing-Nan Lu, and Ulf-G. Meißner, "Emerging geometries and dualities in carbon nuclei," May 15, 2023, Nature Communications. Meißner, May 15, 2023, Nature Communications.

DOI:10.1038/s41467-023-38391-y

Compiled source: ScitechDaily