In the first moments of our universe, the lightest chemical elements were created through a nuclear reaction in a process known as Big Bang nucleosynthesis (BBN). In one key reaction, the fusion of two different atomic nuclei of hydrogen, the proton and the deuterium, formed a stable helium isotope, helium-3. This reaction has been studied with greater precision than ever before by an international research team at the Laboratory for Underground Nuclear Astrophysics (LUNA) at the Gran Sasso National Institute of Nuclear Physics in Italy. A study of the latest breakthrough results in the LUNA experiment has recently been published in the journal Nature.

Nuclear reactions are responsible for the formation of the chemical elements that make up our world. The study of these reactions is one of the most promising areas of research today. By connecting astrophysics with nuclear physics, it forms the interdisciplinary field of nuclear astrophysics.

The LUNA Collaboration’s 400kV underground particle accelerator

The early phase of element formation is the nucleosynthesis of light elements generated immediately after the Big Bang. Understanding this phenomenon also brings us cosmological information about the Big Bang itself, and this has been studied with greater accuracy than ever before by researchers in the LUNA project. Previous experimental nuclear physics findings were not precise enough, as one of the nuclear reactions affecting the amount of deuterium atoms, the fusion of deuterium and proton, was not well known. Due to cosmic radiation reaching the earth’s surface, this kind of experimental study of nuclear reactions of significance to astrophysics is very difficult, and sometimes impossible

In the cosmic silence of LUNA, where 1,400 meters of rock protect the experimental laboratories from external radiation, researchers have been able to recreate the processes that took place during the Big Bang nucleosynthesis, and that still occur in the stars today. With the LUNA particle accelerator, researchers have figuratively gone back in time to a few moments after the birth of the universe. The latest findings of the LUNA Collaboration are that the proton capture in deuterium in the energy domain of post-explosion nucleosynthesis has now been determined with a precision that provides independent information on the initial mass density of the universe.

In an Italian, Hungarian, British and German collaboration, the researchers refined the calculations identified so far with regards to Big Bang nucleosynthesis and pinpointed the density of ordinary, or barionic matter, which is the creator of everything we know in the Universe, including living species. The same density also determines the quantity of deuterium formed during the Big Bang that can be observed by astronomical observations. Until now, these two figures had not been comparable because, despite observations, the experimental nuclear physics data were not sufficiently accurate.

The Nuclear Astrophysics Group of the ELKH Institute for Nuclear Research (Atomki) contributes to the LUNA experiment by participating in experiments at the Italian Institute and by carrying out various additional measurements at Atomki.

The nuclear astrophysicists of the Miklós Konkoly Thege Astronomical Institute (CSFK KTM CSI) of the ELKH Astronomical and Earth Sciences Research Centre participate in the LUNA collaboration with astrophysical model calculations using underground nuclear parameters.

In addition to participating in the LUNA project, researchers from the two Hungarian institutes conduct important research in several fields of astrophysics, such as understanding the chemical composition of meteorite star dust particles, the formation of heavier-than-iron elements, the development and destruction of massive stars and supernovae, and the evolution of the Universe. The researchers will continue their research activities throughout the next decade, including the LUNA-MV project, which will focus on studying reactions that are important for understanding the chemical composition of the Universe and the evolution of stars.

Details of the article:

The baryon density of the Universe from an improved rate of deuterium burning

  1. Mossa et al. (LUNA Collaboration)

NATURE, November 11, 2020

DOI: 10.1038/s41586-020-2878-4

Further infomation:

Dr. Maria Lugaro (maria.lugaro[at]