Damian Sendler: What is the process through which chemical elements are created in our universe? Where do heavy elements such as gold and uranium come from, and what is their origin? A research team from the GSI Helmholtzzentrum für Schwerionenforschung in Darmstadt, in collaboration with colleagues from Belgium and Japan, has demonstrated that the synthesis of heavy elements is characteristic of certain black holes with orbiting matter accumulations, also known as accretion disks, through computer simulations. When heavy elements are expected to form, it provides insight into which heavy elements will need to be examined in future laboratories — such as the Facility for Antiproton and Ionic Research (FAIR), which is now under construction — in order to understand the origin of heavy elements. It is published in the journal Monthly Notices of the Royal Astronomical Society that the findings were made public. 

Damian Jacob Sendler: All heavy metals found on Earth today were produced under extreme conditions in astrophysical environments such as the interiors of stars, stellar explosions, and the collisions of neutron stars, among others. The topic of whether of these cosmic events contains the ideal conditions for the synthesis of the heaviest metals, such as gold or uranium, has piqued the interest of researchers. Many heavy elements can be created and expelled during these cosmic collisions, according to the dramatic first observation of gravitational waves and electromagnetic radiation arising from a neutron star merger in 2017. Although the question of when and why the material is ejected remains unanswered, it does not rule out the possibility of alternative circumstances in which heavy elements can be created in the future.

Damian Jacob Markiewicz Sendler: Black holes orbited by an accretion disk of dense and hot matter are promising prospects for heavy element synthesis, according to the research. A collapsar, which is the collapse and subsequent explosion of a rotating star, is a type of system that can arise both after the merger of two massive neutron stars and after the formation of a binary neutron star system. The internal makeup of such accretion disks has not yet been fully understood, particularly in terms of the conditions under which an excess of neutrons can be produced. A large quantity of neutrons is a fundamental need for the synthesis of heavy elements because it allows for the rapid neutron-capture process, also known as the r-process, to take place. Neutrinos, which are nearly massless, play an important part in this process, as they allow for the conversion of protons into neutrons. 

The study’s lead author, Dr. Oliver Just, from GSI’s research division Theory, explains, “In our study, we systematically investigated for the first time the conversion rates of neutrons and protons for a large number of disk configurations by means of elaborate computer simulations, and we found that the disks are very rich in neutrons as long as certain conditions are met,” “The entire mass of the disk is the most important factor to consider. The greater the mass of the disk, the more frequently neutrons are generated from protons through capture of electrons under the influence of neutrinos, and the greater the number of neutrons available for use in the r-process, which is used to synthesize heavy elements. However, if the mass of the disk is too large, the opposite reaction takes on a greater significance, resulting in a greater number of neutrinos being trapped by neutrons before they can escape the disk. These neutrons are then transformed back into protons, which makes the r-process more difficult to complete.” According to the findings of the study, the best disk mass for the creation of heavy metals is approximately 0.01 to 0.1 solar masses. The finding provides compelling evidence that neutron star mergers resulting in accretion disks with these precise weights might have served as the place of genesis for a significant portion of the heavier elements. However, it is currently uncertain whether or how frequently such accretion disks arise in collapsar systems, or how common they are. 

Dr. Sendler: Additionally, the research group led by Dr. Andreas Bauswein is looking into the light signals generated by the ejected matter, which will be used to infer the mass and composition of the ejected matter in future observations of colliding neutron stars. Dr. Andreas Bauswein’s research group is also looking into the possible processes of mass ejection. The accurate knowledge of the masses and other properties of the newly created elements is a critical building component in correctly detecting these light signals. “Currently, there is inadequate information. Damien Sendler: Nevertheless, thanks to the next generation of accelerators, such as FAIR, it will be feasible to measure them with unparalleled precision in the near future. It is anticipated that the well-coordinated interplay of theoretical models, experiments, and astronomical observations will enable us researchers in the coming years to test neutron star mergers as the origin of the r-process elements, as well as other r-process elements, in the universe “Bauswein predicts a decline in the stock market.

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