Sectional view through the simulation of an accretion disk from the study by Dr. Just and his colleagues.The great void at the center is surrounded by torus-shaped matter a number of hundred kilometers in degree. The rotation axis of the disk is offered by the z-axis, which performs at R= 0 through the black hole along the vertical instructions. The arrows highlight the velocity circulation of the matter. The color shading shows the density (upper left), the proton fraction Ye (lower left), and the characteristic time scales of neutrino emission (upper right) and neutrino absorption (lower right). Values of Ye less than 0.5 show a high fraction of neutrons available for the r-process. Credit: GSI Helmholtz Centre for Heavy Ion Research
” In our research study, we methodically examined for the very first time the conversion rates of neutrons and protons for a great deal of disk configurations by methods of intricate computer simulations, and we found that the disks are extremely rich in neutrons as long as specific conditions are fulfilled,” explains Dr. Oliver Just from the Relativistic Astrophysics group of GSIs research department Theory. “The definitive factor is the overall mass of the disk. The more huge the disk, the more frequently neutrons are formed from protons through capture of electrons under emission of neutrinos, and are readily available for the synthesis of heavy aspects by ways of the r-process. Nevertheless, if the mass of the disk is too high, the inverted reaction plays an increased function so that more neutrinos are regained by neutrons before they leave the disk. These neutrons are then transformed back to protons, which prevents the r-process.” As the research study shows, the optimum disk mass for prolific production of heavy aspects is about 0.01 to 0.1 solar masses. The result provides strong proof that neutron star mergers producing accretion disks with these specific masses might be the point of origin for a big fraction of the heavy elements. However, whether and how frequently such accretion disks happen in collapsar systems is currently unclear.
A crucial structure block for correctly checking out these light signals is precise understanding of the masses and other properties of the freshly formed elements. The well-coordinated interaction of theoretical models, experiments, and huge observations will enable us scientists in the coming years to test neutron star mergers as the origin of the r-process elements,” anticipates Bauswein.
Recommendation: “Neutrino absorption and other physics reliances in neutrino-cooled great void accretion discs” by O Just, S Goriely, H-Th Janka, S Nagataki and A Bauswein, 8 October 2021, Monthly Notices of the Royal Astronomical Society.DOI: 10.1093/ mnras/stab2861.
Neutron-rich product is ejected from the disk, making it possible for the fast neutron-capture procedure (r-process). The light blue area is an especially quick ejection of matter, called a jet, which typically comes from parallel to the disks rotation axis. Credit: National Radio Astronomy Observatory
Using computer simulations, a research team from the GSI Helmholtzzentrum für Schwerionenforschung in Darmstadt, together with coworkers from Belgium and Japan, shows that the synthesis of heavy elements is typical for specific black holes with orbiting matter build-ups, so-called accretion disks. The predicted abundance of the formed aspects offers insight into which heavy aspects require to be studied in future laboratories– such as the Facility for Antiproton and Ion Research (FAIR), which is presently under construction– to unravel the origin of heavy aspects.
All heavy components in the world today were formed under severe conditions in astrophysical environments: inside stars, in stellar explosions, and during the collision of neutron stars. Scientists are fascinated with the question in which of these astrophysical occasions the appropriate conditions for the development of the heaviest aspects, such as gold or uranium, exist. The amazing very first observation of gravitational waves and electromagnetic radiation stemming from a neutron star merger in 2017 recommended that numerous heavy aspects can be produced and released in these cosmic collisions. The concern stays open as to when and why the material is ejected and whether there may be other situations in which heavy aspects can be produced.
Appealing candidates for heavy element production are great voids orbited by an accretion disk of thick and hot matter. Such a system is formed both after the merger of 2 massive neutron stars and throughout a so-called collapsar, the collapse and subsequent surge of a turning star. The internal structure of such accretion disks has up until now not been well comprehended, especially with respect to the conditions under which an excess of neutrons types. A high variety of neutrons is a basic requirement for the synthesis of heavy components, as it allows the rapid neutron-capture process or r-process. Nearly massless neutrinos play a key function in this process, as they enable conversion between neutrons and protons.
Using computer system simulations, a research group from the GSI Helmholtzzentrum für Schwerionenforschung in Darmstadt, together with coworkers from Belgium and Japan, shows that the synthesis of heavy elements is common for particular black holes with orbiting matter build-ups, so-called accretion disks.” In our research study, we systematically examined for the very first time the conversion rates of neutrons and protons for a large number of disk setups by means of intricate computer simulations, and we discovered that the disks are very rich in neutrons as long as specific conditions are fulfilled,” describes Dr. Oliver Just from the Relativistic Astrophysics group of GSIs research division Theory. The more enormous the disk, the more often neutrons are formed from protons through capture of electrons under emission of neutrinos, and are available for the synthesis of heavy components by methods of the r-process. If the mass of the disk is too high, the inverse response plays an increased role so that more neutrinos are regained by neutrons before they leave the disk. The outcome provides strong proof that neutron star mergers producing accretion disks with these exact masses might be the point of origin for a large portion of the heavy aspects.