Observed for the first time in the gas phase: Molecule AcF provides clues to the origin of the universe

AcF is particularly sensitive to so-called CP violations, tiny differences between matter and antimatter that may explain why matter remained after the Big Bang. The study results open up new possibilities to experimentally explore these effects and bring science one step closer to answering the question of why the universe exists.

Breier, until recently at the Institute of Physics at the University of Kassel, was actively involved in the experimental part of the study. The measurements were carried out at the large-scale research facility CERN (European Organization for Nuclear Research) near Geneva. There, the research team irradiated a gas mixture with laser light and analyzed its reactions in order to draw conclusions about the internal structure of the molecules. Together with the lead author of the study, Michail Athanasakis-Kaklamanakis, Breier identified molecular signals for the first time that confirmed that it was indeed AcF in the gas phase. "The signal is complex and still not fully understood, but our modeling of the AcF excitation process provides a consistent picture," explains Breier. "It ultimately provides confirmation: We have observed AcF in the gas phase for the first time."

In the theoretical part of the study, the researchers investigated how well the molecular form of AcF can visualize and amplify CP-injurious effects. The results show that the actinium can act as an amplifier for extremely small CP-violating effects due to its non-spherical but slightly deformed core. As a result, future experiments could make effects accessible that were previously beyond measurability.

Background to the matter-antimatter problem
After the Big Bang, matter and antimatter should actually have annihilated each other completely. Why an excess of matter nevertheless remained is considered one of the greatest mysteries of modern Physics. Researchers suspect that tiny CP violations are responsible for this - effects that are extremely difficult to detect but are considered central to understanding the origin of the universe.

In summary, the study shows that actinium fluoride is a promising molecule for investigating CP effects in more detail in the future. "AcF thus opens up a new way of understanding why the universe looks the way it does," emphasizes Breier.

The paper has been published by Springer Nature: https://www.nature.com/articles/s41586-025-09814-1

What does this mean in summary?

• Dr. Alexander Breier from the University of Kassel took part in an international research project in which the AcF molecule was observed in the gas phase for the first time.
• The AcF molecule reacts particularly sensitively to so-called CP violations, which could possibly explain why more matter than antimatter remained after the Big Bang.
• The results open up new possibilities to investigate these effects experimentally and thus better understand the origin of the universe.