What is the source of gold?  How does our Universe manufacture chemical elements?

A study team has shown that the synthesis of heavy elements is common in some black holes with orbital matter accumulations, known as accretion discs. What heavy elements should be examined in future labs is based on the abundance of the produced elements.


For some black holes, researchers at the GSI Helmholtzzentrum für Schwerionenforschung in Darmstadt, working with colleagues from Belgium and Japan, have shown that the synthesis of heavy elements is common. Future labs, such as FAIR, which is now under development, may use the projected abundance of produced elements to determine which heavy elements need to be investigated in order to understand the genesis of heavy elements. Monthly Notices of the Royal Astronomical Society publishes the findings.

There are three ways in which the heavy metals found on Earth today were created: in the stars, in stellar explosions, and when neutron stars collided. To answer this issue, researchers want to know which of these cosmic occurrences has circumstances that are ideal for the production of gold or uranium. First observations of gravitational waves and electromagnetic radiation emanating from the merging of two neutron stars have shown that heavy elements may be created and released in these cosmic collisions. However, when and why the material is expelled, as well as whether or not heavy elements can be created in other settings, are still up for debate.

Black holes with dense and hot accretion discs are promising possibilities for heavy element generation. A collapsar, the collapse and subsequent explosion of a spinning star, as well as the merging of two massive neutron stars, may both lead to the formation of such a system. Internal composition and circumstances under which an excess neutron population originates are unknown in accretion discs so far. The rapid neutron-capture process, or r-process, requires a large number of neutrons to be present in order to synthesize heavy elements. Protons and neutrons may be converted into each other by neutrinos, which are almost massless.

Researchers at GSI’s research division Theory used sophisticated computer simulations to look into the conversion rates of neutrons and protons for a wide variety of disc configuration. They discovered that discs can contain an abundance of neutrons when certain conditions are met, according to Dr. Oliver Just of the group’s Relativistic Astrophysics.

The disk’s entire mass is the deciding factor. There are more neutrons available for synthesis of heavy elements via the r-process if a disc is large enough to collect electrons from protons and emit neutrinos. Because of this, neutrinos are more likely to be trapped by neutrons before they leave the disc if the disk’s bulk is excessive. The r-process is hampered by the neutrons being transformed back to protons.

Because of this, neutrinos are more likely to be trapped by neutrons before they leave the disc if the disk’s bulk is excessive. The r-process is hampered by the neutrons being transformed back to protons. Heavy element creation is most prolific at roughly 0.01 to 0.1 solar masses, according to the study’s findings. The findings show that neutron star mergers that produce accretion discs with these precise masses might be the origin of a considerable percentage of the heavy elements. However, it is still unknown if and how often collapsar systems have accretion discs.

The light signals formed by the expelled matter are also being studied by the research team lead by Dr. Andreas Bauswein, in order to deduce the mass and composition of the ejected matter in future studies of colliding neutron stars. Knowing the masses and other characteristics of freshly produced elements accurately is a necessary first step in appropriately decoding these light signals. “Currently, this information is lacking. The next generation of accelerators like FAIR will allow us to measure them to unparalleled precision in the future. Neutron star mergers will be tested as a possible origin for the r-process components in the future years thanks to a well-coordinated interaction of theoretical models, experiments and observations” according to what Bauswein says.


O Just, S Goriely, H-Th Janka, S Nagataki, A Bauswein Monthly Notices of the Royal Astronomical Society, Volume 509, Issue 1, January 2022, Pages 1377–1412, https://doi.org/10.1093/mnras/stab2861 Published: 08 October 2021

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